The muscle that is commonly referred to as the "abs" is the rectus abdominis. This is a paired muscle that runs vertically along the anteriorabdominal wall and is responsible for flexing the trunk, compressing the abdominal contents, and supporting the spine. The rectus abdominis is often referred to as the "six-pack muscle" because its paired muscle bellies, separated by tendabdominal wall and is responsible for flexing the trunk and compressing the abdomen. It is also commonly known as the "six-pack" muscle, due to the visible six-pack appearance in physically fit individuals. The rectus abdominis is an important core muscle and is often targeted during exercises such as crunches, sit-ups, and planks.