Quadriceps femoris, or quads, are a group of muscles on the front and sides of the thigh that are responsible for many lower-body movements:
Function
Quads are responsible for knee extension, hip flexion, posture, and maintaining patellar stability. They also help with walking, running, jumping, kicking, and squatting.
Anatomy
Quads are made up of five muscle bellies, including the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. The term "quadriceps" comes from Latin and means "four headed".