GYATT is a term used to describe someone (normally female) with a large booty. Sometimes, this term is used for guys because they might have 2 Jupiter-sized springs on their booty.
example one, female:
person 1: woah, look at that gyatt.
person 2: jeez, that’s a huge gyatt fr.
example two, male:
person 1: OMG I GYATT SOMETHING IN MY EYE.
person 2: OML HE DOES HAVE A GYATT.