I am always bit confused about single mode and multimode fiber cables. The differentiation between them is not so tough to understand. The only difference is the core part.
The core is the highly refractive region of the optical fiber from which the light is trasmitted. According to the ITU the diameter of the single mode fiber should fall between 8 to 10 micron meter and 50 to 62.5 micro meter of multi mode fiber cable.
Now how to remember which cable is used small or large distance. It's also very easy. Think single mode fiber cable is having a very small core where in only a light can transmit, it means a monopoloy of light is there and it could travel upto to a large distance. The multimode fiber cable is having a big core which means more lights could travel in the big core, a quarrel always happen where more than one comes, so no one can survive for a long period of time. Hence MMF cables are used for short distance.