50/125 is one of the most commonly used multimode optical fiber the other most commonly used are 62.5/125 types. The 50 and 125 is measurement by the unit micron. One meter is equal to one million micron. There is a special kind of 50/125 multimode fibers, which are called OM3 50/125. 62.5/125 is usually referred to as the OM1 MMF, common type 50/125 MMF as OM2, OM3 is also 50/125, but it differs from OM2 because it supports 10Gig data transmission. The OM3 50/125 fiber optic cable is also called laser optimized fiber cable. Both OM1 and OM2 multimode cables use the orange color jacket (standard practice for commonly used indoor multimode), OM3 use a special color, which is called Aqua.