Oblique is a term used to describe something that is neither perpendicular nor parallel to a given line or surface, and is instead slanting or sloping. It can also refer to a solid that does not have its axis perpendicular to the plane of the base. In anatomy, oblique muscles are a group of thin, flat muscles that form the middle and outer layers of the lateral walls of the abdomen. Exercises that target the obliques can help to strengthen and tone the muscles along the sides of the trunk.