Rhythmic sliding of the fret hand up and down the neck of a bass guitar to simulate masturbation (i. e., fap). Specifically coined to refer to the bassist's portion of the band intro on Adam Lambert's Glam Nation tour, wherein such motion is often employed.
Did you see last night's concert? When Tommy Joe Ratliff broke out the bassfap during his solo, the Glambulge must have grown six inches.
by aonvas August 1, 2010