The Tibialis Posterior is a muscle found in the lower leg, specifically in the posterior compartment. It helps support the arch of the foot and aids in walking and running. There are several synonyms for this muscle, including the posterior tibial muscle, the tibial muscle, and the deep posterior muscle. Additionally, some sources use the term flexor retinaculum, which is a ligament that helps hold the Tibialis Posterior muscle in place. The muscle is crucial for stability and movement in the lower leg and foot, and it is important to keep it healthy and strong through proper exercise and stretching.