Guitar Pull Off – an already ringing note is released by the players finger to play a lower note on the same string

(Pronounced pul-off)

Note: A guitar pull off is the opposite of a guitar hammer-on.

To remember what a pull off is, it's essentially in the name.

Pull off a note you are holding down

An already ringing note is released by the player's finger, but that finger while releasing, drags/plucks the string again to play a lower note.

As follows:

Image only one string on a guitar place two fingers on your left hand on two separate fret bars and pluck the string at position 1 with your right hand.

Now release your finger at position 2, but while releasing your finger drag/pluck the string again leaving your finger at position 3 in place. 

The reason for using pull off's is that you get slightly different sound than just plucking the string at position 1 again. It also allows you to pluck another string with your right hand at the same time, creating some very interesting sounds and speeding up your playing.