Can be a noun or a verb.
Noun: Something or someone who is cute beyond words! The person seeing this uber-cuteness often makes a high-pitched "PEEEEEE!" or "SQUEEEEE!" sound because he/she/it is just so damn cute!!
Verb: Refers to the act of being cute.
PEEEEEE! There's a mootzie on the fence (referring to a squirrel or some other super-cute animal).
My son, Adam is so mootzie!!