When you look at a mini-dish system, there are two main components that stand out: 1)the round or oval dish itself, and 2)the "arm" which extends out in front of the dish. At the end of the arm is a small "eye" that picks up the satellite signal from the dish, and this "eye" is the LNB. It is the job of the LNB to channel the satellite signal into the cabling that carries the signal from the dish into the house. Dual LNB refers to a specific type of LNB that is equipped to channel the signal simultaneously into multiple receivers. A dual LNB is required for any multi-room system that uses two or more receivers.