What is it?
A pull-off is the opposite of the hammer-on. It is notated as a slurs with the symbol "P" or "Po".
How to play it
It's produced by playing a fretted note and then pulling the left-hand finger off the note to sound a lower note.
Below is an example of pull-off on the G string open. Pick only the first note then pull the string to play the open string.
As you will see in the video, after pulling the string I put my finger on the 2nd string to mute it.
And below the E minor pentatonic scale played with pull-offs.
Pay attention to mute the open strings by putting the finger on them.
Play now this pull-off on the 8th fret.
Place both fret fingers on the two notes to be played.
Play now these pull-offs on the A minor pentatonic scale.
Place both fret fingers on the two notes to be played for every string.
The 1st finger must damp or block an adjacent string to keep it from sounding when a note is pulled-off.
And below two easy nice guitar licks with pull-offs.