Clean Pulls, which can be done from the floor, from just below the knee, or from above the knee (hang clean position). It is meant to build the strength of the muscles that contribute to the "pull" portion of a power clean. This is very valuable for both practice of an important skill, and general strength.

If you are new to this or have trouble maintaining proper form, you should begin with clean pulls from above the knee, then progress to doing them from below the knee and then the floor, as you get better with practice.