An A record in DNS is the fundamental record type used to assign an IP address to a DNS name. Devices on their own do not understand how to communicate with human readable names, and so the DNS server acts as a phone book to make sure we’re “calling” the right number.
The A stands for Address in this case. A records may only be assigned to IPv4 addresses. In the case of IPv6, you will use an AAAA record. The A record will be stored in a DNS zone on a DNS authoritative server usually residing on a company’s network or at a website host company.
If at your company, you had a server with internal information for your employees, you might want to call it internal.yourcompany.com. You would give that server a static IP address. Then on your internal DNS server you would create an A record that assigned internal.yourcompany.com to an IP address of 192.168.10.10 for example.
Once you’ve registered that DNS record, your employees may start using the DNS name instead of the IP address to navigate to it.
There is generally only one A record assigned to a host. Other types of DNS records may be used on that same host, though, such as MX (Mail Exchange), TXT (Text), or a CNAME (Canonical Name) record as well.