A simple INternet search would have brought you to Wikipedia, where the following is stated on DNS Record Classes:
The CLASS of a record is set to IN (for Internet) for common DNS
records involving Internet hostnames, servers, or IP addresses. In
addition, the classes Chaos (CH) and Hesiod (HS) exist.[34] Each class
is an independent name space with potentially different delegations of
DNS zones.
Find the link here.
solved WHAT is “IN” in DNS records? [closed]