The Japanese name for a Karate technique:

type: block

English name: down block


Using the left arm: The right arm is extended in front of you so the fist is level with the solar plexus while the left arm is bent with the fist drawn up near the right ear, palm facing toward the head. At the same time, pull the right arm back into the chamber position and bring the left arm down, leading with the elbow until it's roughly parallel to your front leg while pivoting on the elbow to extend the forearm, twisting at almost the last moment so the palm is facing the knee and about ten centimeters above it, (assuming you're using zenkutsu-dachi). As you do this, move the hips, thrusting the left hip forward and the right back.

This block protects the groin, abdomen, and upper legs. The idea is to strike the arm, leg, or 2x4 that is attacking your lower region, changing it's trajectory before it impacts you. In addition to a block, it is also used widely as a part of assuming a stance. When assuming zenkutsu dachi for kihon gedan barai is almost always performed as the stance is assumed. This increases readiness since you perform a technique before you're even engaged, like swordsmen who are trained to slice the air in front of them every time they remove their blade from the scabbard, even the unsheathing of the weapon is an attack.