The board has 4 channels, each ram slot is a channel. single, dual, triple, and quad is how the channels or slots are connected.
Quad handles data faster.
Single Channel (64bit) = one ram slot. On a board with 4 slots the use of the ram would saturate one stick of ram before going to the next. Each slot connected back to the controller with 64 wires.
Dual Channel (128bit) = 2 slots acting as one. On a board with 4 slots, slots 1 and 3 are paired, slots 2 and 4 are paired. Each slot still connected with 64 wires, but since the controller can do 128, two channels used at the same time to fill the 128. Once pair 1/3 is saturated it will move to pair 2/4
Triple Channel (192bit) = 3 slots acting as one. Board in 3,4, or 6 slot configurations. Working in sets of 3 sharing the data load. If you used 4 sticks in a triple channel board it drops back to dual channel. In 6 slot config paired slots are 1/3/5 and 2/4/6, once 1/3/5 are saturated, 2/4/6 comes into play.
Quad Channel (256bit) = 4 slots acting as one. Board has 4 or 8 slots. Working in sets of 4 sharing the data load. In the 8 slot config paired slots are 1/3/5/7 and 2/4/6/8.