Definition of Rectus abdominis

Rectus abdominis: A large muscle in the front of the abdomen that assists in the regular breathing movement and supports the muscles of the spine while lifting and keeping abdominal organs such as the intestines in place. The rectus abdominis plays a key role in "sit-ups."

Rectus means straight. The rectus abdominis is a straight abdominal muscle. It is sometimes simply called the rectus.