Yoko-geri is the Japanese term for the side kick, a basic kick in many martial arts styles. A famous, more advanced form of yoko-geri is flying side kick. Yoko-geri one of Jack's best kicks in Taijutsu.
How to execute a side kick
Step One: Starting in sparring stance (body sideways), pick up the back leg.
Step Two: Just as with roundhouse kick, turn your hips and pivot on the other foot.
Step Three: Kick straight out, aiming with your heel, making sure both sections of your leg straighten at the same time. Otherwise, the kick will not be a side kick but a poorly executed roundhouse kick.
Just as with any kick, side kick can also be done with the front leg. A front leg side kick follows similar steps:
Step One: Starting in sparring stance, pick up the front leg.
Step Two: Turn your hips and kick straight out, aiming with your heel. Your entire leg should straighten all at once. You will pivot as you kick rather than before you kick, since it is the front leg you are kicking with.