Single mode and multi mode are two types of fiber optic cables. Single mode fiber has a small core diameter of 8-10 microns and is used for long distance data transmission. It is capable of transmitting data over distances of up to 10km. Multi mode fiber has a larger core diameter of 50-100 microns and is used for shorter distance data transmission. It is capable of transmitting data over distances of up to 2km. Single mode fiber is more expensive than multi mode fiber, but it is more reliable and offers higher bandwidth.