A forward DNS lookup is a dns lookup that translate a DNS name to an IP.
The inverse is called a reverse lookup
A forward DNS lookup is a query executed by a resolver that will lookup in order:
and return the first IP found.
For example, the domain name www.example.com translates to the addresses 192.0.32.10 (IPv4) and 2620:0:2d0:200::10 (IPv6).
Every time you visit a website, your browser performs a forward DNS lookup to get the web page. Complex web pages that includes different resource (image, script,..) often require multiple DNS lookups before they start loading, so a computer may be performing hundreds of lookups a day.