Obturator internus is a muscle located in the pelvic area that aids in external rotation of the hip joint. It is also known as the internus obturator, internus obturatorius, and obturatorius internus. The muscle is part of the hip adductor group of muscles and is surrounded by the obturator membrane and the obturator externus muscle. Additionally, it is responsible for lateral rotation of the hip joint and maintaining the stability of the pelvis. Understanding the various synonyms for the obturator internus helps facilitate communication between healthcare professionals, students, and patients. Knowing the various names for muscles and other anatomical structures is integral to learning anatomical terms.