An expert in playing an electric bass guitar by plucking it with his/her fingers, instead of using a pick. Veteran motherpluckers devellop tremendous finger and arm strength to pluck hard and fast. The term can be extended to 'mean motherplucker'.
Examples of motherpluckers:
Robert Trujillo of Metallica
Flea of Red Hot Chili Peppers
Lyn-Z of Mindless Self Indulgence