Something that's trimmed has been cut or clipped to be tidier or smaller in size. Your dad's trimmed beard makes him look especially handsome in the tuxedo he's wearing to your cousin's wedding.
A trimmed lawn has been mowed recently, leaving the grass short and tidy. A trimmed budget has been figuratively cut, with the unnecessary expenses removed. A trimmed Christmas tree has been decorated, while the trimmed sails on a sailboat have been adjusted. The adjective trimmed and verb trim come from the Old English trymian, a word whose meanings include "set in order" and "arrange."