The side teep is a thrust kick which was once considered to be the most dangerous and effective kick during the height of traditional martial arts popularity.
The side kick to the abdomen can be a difficult kick to land, and easily parried. Consequently this kick can be risky because a missed strike or glancing blow to your opponents torso results in giving up your back.
Recently MMA technicians such as Jon Jones and Anderson Silva have utilized this technique to keep their opponents at range and outpoint them easily, primarily relying on a lead side teep to the front of the knee.
Check out a deep dive into the side kick on the next page, with a video citing examples of usage in real fights:
Page 1 of 2: