When you search for something and click on one of the tabs
the resulting URL contains a searchOn parameter:
https://meta.stackexchange.com/search?tab=newest&q=something&searchOn=3. If I recall correctly, that was added when Stack Overflow for Teams was integrated into Stack Overflow, where you could choose whether to search on the public site only, Teams only, or both. Since all sites in the network share the same codebase, it shows here on Meta too. Now that Teams has been decoupled from Stack Overflow, the parameter does not serve any purposes, and since shorter URLs are better[citation needed], the parameter can be removed.
