Glossary
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Plain-language definitions of the DNS, domain, SSL and infrastructure terms you'll actually run into.
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DNS
20- A recordAn A record is a DNS resource record that maps a domain name to an IPv4 address (32-bit number), enabling browsers and applications to find your server on the internet.
- AAAA recordAn AAAA record is a DNS record that maps a domain name to a 128-bit IPv6 address, serving as the IPv6 counterpart to the A record.
- Anycast DNSAnycast DNS is a routing technique where multiple servers share the same IP address, automatically directing queries to the geographically or topologically nearest server.
- Authoritative DNS ServerAn authoritative DNS server holds the actual zone data for a domain and answers DNS queries directly from its own records, not from cache.
- CAA recordA CAA record is a DNS record type that authorizes which Certificate Authorities are permitted to issue TLS/SSL certificates for a domain.
- CNAME recordA CNAME record is a DNS record that maps an alias hostname to its canonical (true) hostname, causing resolvers to look up the target name instead.
- DNSDNS (Domain Name System) is a hierarchical, distributed database that translates human-readable domain names like example.com into IP addresses and other resource records needed to locate services on the internet.
- DNS FailoverDNS Failover is a high-availability technique in which a DNS provider monitors the health of backend endpoints and automatically directs traffic away from failed services by updating which IP address it returns in DNS responses.
- DNS over HTTPS (DoH)DNS over HTTPS (DoH) is a protocol that encrypts DNS queries by sending them over HTTPS instead of unencrypted UDP, protecting query privacy from network observers.
- DNS propagationDNS propagation is the time it takes for a DNS record change to become visible everywhere, caused by the delay until cached copies of the old record expire at each resolver.
- DNS ResolverA DNS resolver is software or a service that accepts DNS queries from clients and returns answers by iteratively querying authoritative nameservers and caching the results.
- DNS ZoneA DNS zone is an administratively autonomous portion of the DNS namespace, defined by delegation, for which a specific set of nameservers is authoritative and which contains a SOA record at its apex.
- DNSSECDNSSEC (DNS Security Extensions) is a suite of protocols that add digital signatures to DNS records, allowing resolvers to verify that DNS responses are authentic and unmodified.
- MX recordAn MX record is a DNS resource record that specifies the mail server responsible for accepting email on behalf of a domain.
- NS recordAn NS record is a DNS resource record that identifies which name servers are authoritative for a domain or subdomain.
- Reverse DNSReverse DNS (rDNS) is the DNS lookup process that resolves an IP address back to a domain or hostname using PTR records, the inverse of a normal forward DNS lookup.
- SOA RecordAn SOA (Start of Authority) record is a mandatory DNS record that marks the beginning of a zone, identifies the primary nameserver, and specifies zone administration and transfer parameters.
- SRV RecordAn SRV record is a DNS record type that specifies the hostname and port number for servers providing a specific service, enabling service discovery without hardcoded addresses.
- TTLTTL (Time To Live) is a numeric field in every DNS record specifying the maximum number of seconds a resolver or cache can store that record before it must be re-fetched from the authoritative nameserver.
- TXT recordA TXT record is a DNS resource record that stores arbitrary text data associated with a domain, commonly used for email authentication policies, domain verification, and other machine-readable configuration.
Domains
18- Apex domainAn apex domain is the root domain name without any subdomain prefix, such as example.com rather than www.example.com, and must host the SOA and NS records for the DNS zone.
- Country-Code Top-Level Domain (ccTLD)A country-code top-level domain (ccTLD) is a two-letter domain extension assigned to a specific country or territory, such as .uk for the United Kingdom or .jp for Japan.
- Domain BackorderA domain backorder is a paid service that automatically attempts to register a domain name the moment it expires and becomes available for re-registration.
- Domain registrarA domain registrar is an ICANN-accredited business that sells domain names and manages registrations on behalf of customers by communicating with the authoritative registry for each top-level domain.
- Domain RegistryA domain registry is the centralized database and administrative authority that maintains the authoritative record of all registered domain names under a specific top-level domain (TLD) and manages the technical infrastructure for those domains.
- Domain TransferA domain transfer is the process of moving a domain name from one registrar or owner to another, involving authorization codes and DNS record preservation.
- Drop-CatchingDrop-catching is the practice of monitoring expiring domain names and attempting to register them the moment they become available for public registration, typically using automated systems that submit registration requests at high speed.
- EPP Code (Auth Code)An EPP Code (also called Auth Code or AuthInfo code) is a unique authorization password generated per domain at the registry level to prove that a domain transfer or registrant action is approved by the domain's current owner.
- Generic Top-Level Domain (gTLD)A Generic Top-Level Domain (gTLD) is a top-level domain that is not restricted to a country or territory, such as .com, .org, .net, or newer options like .tech and .app.
- Glue recordA glue record is an A or AAAA record that a parent DNS zone publishes alongside a nameserver delegation to provide the IP address of a nameserver whose hostname is within the delegated child domain.
- ICANNICANN (Internet Corporation for Assigned Names and Numbers) is the nonprofit organization that coordinates the global domain name system, IP address allocation, and internet protocol parameters.
- Internationalized Domain Name (IDN)An Internationalized Domain Name (IDN) is a domain name that contains non-ASCII characters, such as accented letters or characters from non-Latin scripts, enabling domain registration in languages other than English.
- NameserverA nameserver is a server that stores DNS records for a domain and answers queries to resolve domain names into IP addresses and other zone data.
- Redemption Grace PeriodRedemption Grace Period is a 30-day window after a domain expires during which the registrant can still recover and renew it, usually at standard renewal cost rather than a penalty fee.
- Registrar LockRegistrar Lock is a status flag set by a domain registrar that prevents the domain from being transferred, updated, or deleted without explicit authorization to remove the lock first.
- SubdomainA subdomain is a domain name that is subordinate to a registered domain in the DNS hierarchy, created by prepending one or more labels to the parent domain (e.g., mail.example.com is a subdomain of example.com).
- Top-Level Domain (TLD)A Top-Level Domain (TLD) is the rightmost part of a domain name, such as .com, .org, or .uk, that sits at the highest level of the DNS hierarchy.
- WHOISWHOIS is a protocol and database system that records and makes publicly queryable the registration details of domain names, including registrant information, registrar, creation/expiration dates, and nameservers.
- BIMIBIMI (Brand Indicators for Message Identification) is an email specification that allows a sender's logo to display next to authenticated messages in supporting email clients.
- DKIMDKIM (DomainKeys Identified Mail) is an email authentication method that uses cryptographic signatures to verify that a message was sent from and authorized by a specific domain, and that its content was not altered in transit.
- DMARCDMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication policy protocol that lets a domain owner publish a DNS record instructing receiving mail servers how to handle messages claiming to be from that domain that fail SPF and DKIM checks.
- Email DeliverabilityEmail deliverability is the measurable ability of an email to reach a recipient's inbox rather than the spam folder or being rejected, determined by sender reputation, authentication status, and infrastructure signals.
- MTA-STSMTA-STS (SMTP MTA Strict Transport Security) is a standard that lets email domain owners publish a policy requiring mail servers to deliver messages only over encrypted TLS connections, preventing downgrade attacks.
- SMTPSMTP (Simple Mail Transfer Protocol) is the Internet standard protocol used to transmit and relay email between mail servers and from clients to mail servers for sending.
- SPFSPF (Sender Policy Framework) is an email authentication protocol that publishes a DNS TXT record listing IP addresses and servers authorized to send email on behalf of a domain, allowing receiving mail servers to verify the sender's identity.
SSL/TLS
15- ACME ProtocolACME Protocol is an automated standard for requesting, validating, and renewing SSL/TLS certificates between a client and a Certificate Authority.
- Certificate authorityA certificate authority (CA) is a trusted entity that issues and digitally signs SSL/TLS certificates after verifying the identity of the requester, establishing a cryptographic chain of trust.
- Certificate ChainA certificate chain is an ordered sequence of X.509 digital certificates linking a server's end-entity certificate to a trusted root Certificate Authority, where each certificate is signed by the next one in the chain.
- Certificate Signing Request (CSR)A Certificate Signing Request (CSR) is a formatted message containing a public key and identifying information that an applicant sends to a Certificate Authority to request issuance of an SSL/TLS certificate.
- Certificate TransparencyCertificate Transparency is an open framework that logs all newly-issued TLS certificates to public, append-only registries, allowing detection of misissued or malicious certificates.
- HSTSHSTS (HTTP Strict Transport Security) is an HTTP header that instructs browsers to only access a website over HTTPS, automatically upgrading any HTTP requests to secure connections.
- HTTPSHTTPS is HTTP layered over TLS encryption, ensuring confidential and authenticated communication between a browser and web server using an X.509 certificate.
- Let's EncryptLet's Encrypt is a free, automated nonprofit Certificate Authority that issues domain-validated SSL/TLS certificates via the ACME protocol.
- OCSP StaplingOCSP Stapling is an SSL/TLS optimization where a web server includes a time-stamped OCSP response from the certificate authority directly in the TLS handshake, eliminating the need for clients to contact the OCSP responder separately.
- SAN CertificateA SAN certificate is an X.509 SSL/TLS certificate that secures multiple hostnames, domains, or IP addresses under a single certificate using the Subject Alternative Name (SAN) extension.
- Server Name Indication (SNI)Server Name Indication (SNI) is a TLS extension that allows a client to specify the hostname it is connecting to during the initial TLS handshake, enabling multiple HTTPS certificates to be served from a single IP address.
- SSL certificateAn SSL certificate is a digital credential signed by a Certificate Authority that binds a public cryptographic key to a domain name, enabling servers to prove their identity and establish encrypted TLS connections with clients.
- SSL/TLSSSL/TLS is a cryptographic protocol that encrypts and authenticates data transmitted over networks, securing communication between clients and servers.
- TLS HandshakeA TLS handshake is the cryptographic negotiation protocol in which a client and server authenticate, agree on encryption parameters, and derive shared session keys before exchanging encrypted application data.
- Wildcard certificateA wildcard certificate is an SSL/TLS certificate with a hostname containing a leading asterisk (e.g., *.example.com) that secures an unlimited number of first-level subdomains with a single certificate.
Monitoring
9- Health CheckA health check is an automated periodic probe sent to a service or endpoint to verify it is operational and ready to receive traffic.
- Heartbeat MonitoringHeartbeat monitoring is the periodic transmission of a lightweight signal from a monitored system to confirm it is still running and responsive.
- IncidentAn incident is a detected event indicating unplanned service disruption, degradation, or security violation that requires investigation and response.
- Maintenance WindowA maintenance window is a scheduled time period during which expected system changes—such as updates, patches, or deployments—occur, and monitoring alerts are temporarily suppressed to prevent false incident notifications.
- MTTR (Mean Time to Recovery)MTTR (Mean Time to Recovery) is the average time it takes to restore a failed system or service to full operational status, measured from the moment of failure to complete recovery.
- SLAAn SLA (Service Level Agreement) is a formal, measurable commitment between a service provider and customer defining expected performance levels such as uptime percentage, response time, and support response times.
- Status PageA status page is a public or private web page that displays the real-time operational state of a service's components and communicates incidents, maintenance, and uptime to users.
- Synthetic MonitoringSynthetic monitoring is a proactive technique that simulates user interactions with a system on a scheduled basis from external vantage points to measure availability, performance, and correctness.
- Uptime monitoringUptime monitoring is automated, repeated checking of a server, website, or service at regular intervals to detect when it becomes unavailable and alert you to outages.
Network
10- CIDR NotationCIDR notation is a compact way to write an IP address and its network prefix length as address/bits (e.g., 192.168.1.0/24), replacing older class-based addressing to enable flexible subnetting and route aggregation.
- Content Delivery Network (CDN)A Content Delivery Network (CDN) is a geographically distributed system of servers that caches and delivers web content from locations closer to end users, reducing latency and improving load times.
- Dynamic DNSDynamic DNS (DDNS) is a method that automatically updates DNS records when an IP address changes, allowing a hostname to stay current without manual edits.
- IPv4IPv4 (Internet Protocol version 4) is the fourth version of the Internet Protocol, using 32-bit addresses to route packets across networks and the internet.
- IPv6IPv6 is the successor to IPv4, using 128-bit addresses instead of 32-bit addresses to provide vastly more available addresses for internet-connected devices.
- LatencyLatency is the time it takes for a packet of data to travel from a source to a destination across a network.
- Load BalancerA load balancer is a network device or service that distributes incoming traffic across multiple servers to improve performance, reliability, and capacity.
- Reverse ProxyA reverse proxy is a server that sits between client requests and backend servers, forwarding requests on behalf of clients while masking the identity and location of the actual application servers.
- Subnet MaskA subnet mask is a 32-bit number that divides an IPv4 address into network and host portions by using binary ANDing, where 1-bits identify the network/subnet part and 0-bits identify the host part.
- TracerouteTraceroute is a network diagnostic tool that maps the sequence of routers (hops) a packet travels through to reach a destination and measures the latency to each hop.
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