Glossary

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Plain-language definitions of the DNS, domain, SSL and infrastructure terms you'll actually run into.

DNS14 Domains10 Email3 SSL/TLS10 Monitoring3 Network8

DNS

A record: An 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 record: An 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.
CAA record: A CAA record is a DNS record type that authorizes which Certificate Authorities are permitted to issue TLS/SSL certificates for a domain.
CNAME record: A 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.
DNS: DNS (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 propagation: DNS 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.
DNSSEC: DNSSEC (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 record: An MX record is a DNS resource record that specifies the mail server responsible for accepting email on behalf of a domain.
NS record: An NS record is a DNS resource record that identifies which name servers are authoritative for a domain or subdomain.
Reverse DNS: Reverse 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 Record: An 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 Record: An 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.
TTL: TTL (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 record: A 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

Apex domain: An 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 registrar: A 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.
Drop-Catching: Drop-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.
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 record: A 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.
Nameserver: A 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.
Subdomain: A 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.
WHOIS: WHOIS 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.

Email

DKIM: DKIM (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.
DMARC: DMARC (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.
SPF: SPF (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

ACME Protocol: ACME Protocol is an automated standard for requesting, validating, and renewing SSL/TLS certificates between a client and a Certificate Authority.
Certificate authority: A 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 Transparency: Certificate Transparency is an open framework that logs all newly-issued TLS certificates to public, append-only registries, allowing detection of misissued or malicious certificates.
HSTS: HSTS (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.
HTTPS: HTTPS is HTTP layered over TLS encryption, ensuring confidential and authenticated communication between a browser and web server using an X.509 certificate.
Let's Encrypt: Let's Encrypt is a free, automated nonprofit Certificate Authority that issues domain-validated SSL/TLS certificates via the ACME protocol.
SSL certificate: An 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/TLS: SSL/TLS is a cryptographic protocol that encrypts and authenticates data transmitted over networks, securing communication between clients and servers.
TLS Handshake: A 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 certificate: A 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

SLA: An 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 Page: A 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.
Uptime monitoring: Uptime 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

CIDR Notation: CIDR 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 DNS: Dynamic DNS (DDNS) is a method that automatically updates DNS records when an IP address changes, allowing a hostname to stay current without manual edits.
IPv4: IPv4 (Internet Protocol version 4) is the fourth version of the Internet Protocol, using 32-bit addresses to route packets across networks and the internet.
IPv6: IPv6 is the successor to IPv4, using 128-bit addresses instead of 32-bit addresses to provide vastly more available addresses for internet-connected devices.
Load Balancer: A load balancer is a network device or service that distributes incoming traffic across multiple servers to improve performance, reliability, and capacity.
Reverse Proxy: A 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 Mask: A 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.

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