A person's thigh is composed of three major muscles: the quadriceps, hamstrings and adductors. Typically, when someone refers to the thigh muscle, the person is speaking about the quadriceps.
The quadriceps is a muscle group that is found on the top of the thigh. It is used in hip flexion and knee extension, while the hamstrings muscle group has the opposite function. Most leg bending movements like running or walking are controlled by a combination of the quadriceps and hamstring muscles. The adductors are commonly referred to as the groin and are used in lateral movements to pull the legs together.