OM3 multimode cable is a fiber patch cable made of OM3 multimode fiber plus indoor or outdoor sheathing, which is often used for building trunk laying and trunk connection between two buildings in close proximity.
OM stands for Multi-mode fibre (also known as MMF), which usually has four levels of OM1/OM2/OM3/OM4, the main difference is the mode bandwidth of the 850nm transmission window.