Wikipedia Search box - advanced
Wikipedia special search box
Special search box just for Search, with the general search domains listed below. Click on one to search that domain.
Some Wikipedia simplified search options
Clicking on Advanced shows the namespaces of the wiki. Check namespaces to set either your current or your default search domain.

There are numerous advanced Search engine features available to help locate what you are looking for within Wikipedia.

Read more:

Help:Searching
Search engine (computing)
Wikipedia industrial-powered search