Slapping is a bass technique where you hitting the string with your thumb near the start of the neck, often pulling or snapping the higher strings with your index and middle finger (popping). This technique first appeared in the 1970s and was synonymous with the funk music of that period. Larry Graham, bassist with Sly and the Family Stone, was one of the bass slapping pioneers. The eighties saw a new generation of slappers, like Mark King of Level 42.

The percussive sound the string makes when it is slapped against the fretboard makes for a rhythmical sound, almost like drumming. Carl Shepard,a bass instructor from Cincinnati, has put together a series of instructional bass videos. Here are some of the slapping and muting ones:

http://www.expertvillage.com/videos/bass-guitar-double-thumb.htm

http://www.expertvillage.com/videos/bass-guitar-slap-techniques.htm

http://www.expertvillage.com/videos/bass-guitar-slap-mute.htm