Pull-ups use the opposite grip from chin-ups. The basic version is the dead-hang pull-up, which starts at full rest and extension at the bottom and finishes with the chin above the grip, with the arms in full contraction, moving across the entire range of motion and using no kicking or swinging to create momentum.
Variants include kipping pull-ups (kicking or swinging the body), assisted pull-ups (using a band, having another person push, or using an assistance machine), one-arm pull-ups, and partial range-of-motion pull-ups. Changing the grip also creates many variants. Fat-grip, towel-grip, and gi-grip (for martial arts like judo or jiu-jitsu) pull-ups are all useful for focusing on grip strength.