Semimembranosus is a muscle located in the back of the thigh. It is part of the larger group of muscles known as the hamstrings. While semimembranosus is the most commonly used term for this muscle, there are a few other synonyms that can be used to describe it. These include the membranous semitendinosus, the half-membranous muscle, and the semimembranous tendon. Each of these synonyms describes the same muscle, but uses different words to do so. Regardless of the terminology used, the semimembranosus muscle is an important part of the human anatomy and plays a critical role in human movement and everyday activities.