A record
AThe A record maps a hostname to an IPv4 address. It is the record most domains cannot work without.
What an A record does
An A record answers one question: which IPv4 address serves this name? A resolver asked for example.com returns the address in the A record, and the client connects to it.
The record type is defined in RFC 1035, and the value is always a bare IPv4 address — never a hostname, and never a URL.
Multiple A records
A name can publish several A records. Resolvers may return them in any order, and clients generally try the first one they receive, so publishing several is a common way to spread traffic across servers.
This is not load balancing in any strict sense. Nothing measures server health, and a client that caches one address will keep using it until the TTL expires.
The apex is different
The apex of a domain — example.com with no subdomain — must carry NS and SOA records. Because a CNAME cannot coexist with other records at the same name, the apex cannot be a CNAME, which is why an A record is usually the only option there.
Some DNS providers offer a flattening feature that resolves a target name and publishes the result as A records at the apex. That is a provider behaviour rather than a DNS feature, so it varies.
TTL and change propagation
Every A record carries a TTL: the number of seconds a resolver may cache the answer. Changing the address does not push anything to resolvers — they keep serving the cached value until it expires.
The practical wait after a change is bounded by the TTL that was in effect before the change, not the one set afterwards. Lowering the TTL a day ahead of a migration is what makes the cutover quick.