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2.
A technique of playing bass, commonly used by Funk bassists and reggae bassists.

It is played with the fingers, and is used to create a popping sound from the string hitting the pickups. The player usually plucks less than the average bassist, and rather uses hammer ons and pull offs
Flea is usually known as the best bassist ever, because he plays slap bass instead of picking.
by Bob Johnski June 14, 2011
 
1.
the most badass way to play the bass guitar.
Flea plays slap bass. OOOOOH YEAHHHHH!
by wowser77 October 28, 2009