It hides all events that don't contain the word somewhere inside it, or it's sub-events.
If the word is mentioned a lot, you will see a lot of events. If it's only in 1, only that one will show, and all others will be hidden. You have to cancel the search to get the others to show again.
I add Search to my "Quick Access Toolbar" along the top edge, so it's present no matter what tab is open.
One glitch, if you are at the bottom of a long event sheet, and do a search, you may have to scroll up to see any of the results.