This command allows the router to assume that any non-keyword entered in the command console is supposed to be resolved into an IP address. This is a default command.
Most people disable this command as it can be a frequent annoyance to those who mistype words on a regular basis.
In this example command that doesn’t exist is accidentally typed in. The router attempts to resolve this unrecognized command as an ip address, and takes awhile to do so. We disable this feature afterwards with no ip domain-lookup.