The Vesica Piscis is mathematically a type of lens, a shape formed by the intersection of two same sized circles. In Latin, "vesica piscis" literally means "bladder of a fish", reflecting the shape's resemblance to the linked dual air bladders ("swim bladder") found in most fish. In Italian, the shape's name is mandorla ("almond").
The symbol can be seen throughout Pythagorean history and was considered a holy figure because the ratio of its width to its height was believed to be 165:153 or 1.73203—a holy number. It should be noted that the number 153 is written in the Gospel of John as the number of fish that Jesus miraculously caught. Because of this, some believe that it is the symbol for Jesus Christ (Ichthys).