Reverse lookup is the process of determining the domain name associated with a given IP address. This can be useful for a variety of purposes, such as identifying the source of spam email, tracking down the owner of a website, or simply finding out more information about a particular IP address.
There are a number of different ways to perform a reverse lookup. One common method is to use a dedicated reverse lookup tool, such as the one provided by Whois.com. These tools typically allow you to enter an IP address and receive the corresponding domain name.