Pull-off is a technique to play legato on a stringed instrument. Two fingers of the fret hand pluck one string. Immediately afterwards, the finger on the higher fret is pulled off the resonating string, causing the original sound to change into the sound of the lower fret which is still plugged (or open). Thus, a seamless transition from a higher to a lower note is effected. (For the contrary, see hammer-on.)

Legato (with pull-off)
Staccato (without pull-off)