Cryopumping is a method of creating ultra-high vacuum in a chamber.
The term "cryopump" is somewhat of a misnomer, as the gases aren't actually pumped. Instead, liquid nitrogen or another cryogenic gas is pumped into the top of the chamber and run along the walls, and finally removed from the bottom. Any stray atoms in the chamber eventually hit the side of the chamber, generally sticking to the liquid and running out with it.
Cryopumping is used far below pressures where other pumping methods are useful.