fetch; English Slang- (adjective) synonyms: nice, fresh, slay, attractive, desirable, cool
Context and meaning
This slang word is used by Gretchen Wieners, one of the plastics from Mean Girls. It means something like desirable, cool, nice and fresh. Apparently, when using this word in context, something or someone is so cool, or slay, that it particularly catches the eye and leaves a very good impression.
Fetch is a positive word, and isn't really used to describe or highlight negative characteristics.