Used as a greeting, a more emphatic and energetic version of "hello"
"Boom selecta! What's going on dude"
Boom Selecta is synonymous with DJ or disk jockey. This can be any person at any level who is choosing the music for a party, club, or social event. In proper English it would be Boom Selector, however Selecta sounds better. In other words, a Boom Selecta is someone who selects mad booms.
Yo! Boom Selecta play dat new Wayne track.