For legs, we will address knee flexion and extension, and ankle planterflexion and dorsiflexion. In fact, let's get it out of the way right now.
Extension is when bones move away from each other at a joint.
Abduction is movement away from the midline of the body. Adduction is movement toward the midline of the body. Dorsiflexion is movement of the toes toward the shin. Plantarflexion is pointing the toes. There are also some rotational movements from the hip, but we won't be concerned with them.