Definition
An A record is a DNS entry that maps a hostname to an IPv4 address, the number a browser looks up to find the right server. It is the simplest and most fundamental DNS record type: when example.com has an A record pointing to 76.76.21.21, that is the address browsers look up when someone visits the domain. Each A record is one line in a zone file: a hostname, the record type, a TTL (cache duration in seconds, commonly 300 to 86400), and the target IPv4 address. A hostname can hold several A records for load balancing or failover, and subdomains need their own entries. AAAA records do the same job for IPv6. Every domain serving web traffic needs at least one A or AAAA record, though CNAMEs often handle subdomains instead. You edit A records inside your registrar or DNS provider's panel (Cloudflare, Route 53, Namecheap, Google Domains); changes propagate worldwide within minutes to a few hours depending on TTL.
How it works
An A record is one line in a zone file: a hostname, the record type (A), a TTL (cache duration in seconds), and the target IPv4 address. A single hostname can have multiple A records for load balancing; subdomains have their own A records.
Why it matters
When you move a website to a new host, the change is an A record update. When a site goes down because DNS was misconfigured, an A record is usually the cause. Understanding how to read, change and verify A records is the most basic DNS skill.