The linea alba (Latin, white line) is a fibrous structure that runs down the midline of the abdomen in humans and other vertebrates. In humans linea alba runs from the xiphoid process to the pubic symphysis. The name means white line and the linea alba is indeed white, being composed mostly of collagen connective tissue.
It is formed by the fusion of the aponeuroses of the abdominal muscles, and it separates the left and right rectus abdominis muscles. In muscular individuals its presence can be seen on the skin, forming the depression between the left and right halves of a "six pack."