The erector spinae (sometimes known as sacrospinalis) is often described as a group of different muscles called iliocostalis, longissimus and spinalis.
Multifidus is a series of small muscles which travel up the length of the spine. It is an important muscle in the rehabilitation of Gilmore's Groin.
Rectus Abdominus is the most superficial of the abdominal muscles. It is this muscle which forms the six-pack shape!
Transversus Abdominus is often abbreviated to TVA. This is a very important core muscle which is vital in maintaining good posture. Activities such as Pilates focus on contraction of the TVA.
The quadratus lumborum muscle is a common muscle involved in lower back pain.