There is no definition by way of words. It is more of a feeling built up with a certain tension that manifests into a climactic blackhole of speechless expression... this blackhole can only be metaphorically constructed by speech with the so called 'word'...."booyah."
If "booyah" was in a thesaurus, it MIGHT have like terms such as:
-"You just got served!"
-"Oh my God, the quarterback is toast!"
...and in Spanish, the translation of "booyah" would be:
-"Toma!" (which roughly translates into "Take That!")