50/125 is one of the most commonly used multimode optical fiber; the other commonly used is 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 50/125 multimode fibers, which is called OM3 50/125. People usually refer 62.5/125 as the OM1 MMF, common type 50/125 MMF as OM2, OM3 is also 50/125, but it is different from OM2 because it support 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.