A hammer-on is a technique where, after picking a string, you press it firmly with another finger to sound the next note. A pull-off is a technique where you release a fretting finger to sound a lower note.
The basic idea
Because you do not pick every note again with your picking hand, you can create smooth, fast phrases. The key is to organize the movement of the fretting hand so that the attack of each note is even.
Using them in performance and programming
Go slowly back and forth between two neighboring notes and match their volume and timing. Use them inside a legato phrase and mix them with picked notes to add expression.
Difference from related terms
Hammer-ons and pull-offs connect notes with the fretting hand. A slide also connects notes smoothly, but the way the finger moves is different.
They work best when you treat them as a way to shape the texture of connected notes, not only as a way to play fast.
