What "prusik knot" means in rock climbing

A Prusik knot is a knot used in rock climbing as a self-locking mechanism that a climber can attach to a fixed rope to ascend or descend it. It consists of a loop of cord or webbing tied in a special way that grips onto the rope when tension is applied, but can easily be slid up or down on the rope when it is not. The Prusik knot is an essential skill for climbers who want to conduct rescues, set up anchors and belays, or ascend a rope.