They're bangs — shortcuts to directly search on a particular website.

> For example, searching Kagi for !w Monty Python will search Wikipedia directly for "Monty Python" and take you to that Wikipedia search result. [1]

If you're on a plan with limited searches per month, it does not count against your quota.

DuckDuckGo has bangs as well.

[1] https://help.kagi.com/kagi/features/bangs.html