As interjections the difference between what and wassat
is that
what is while
wassat is (slang) what is that?.
As a pronoun what
is (interrogative) which thing, event, circumstance, etc: used interrogatively in asking for the specification of an identity, quantity, quality, etc.
As an adverb what
is in some manner or degree; in part; partly; usually followed by
with .
As a determiner what
is which; which kind of.
As a noun what
is (obsolete) something; thing; stuff.