Basically what he means is that if you have a single AP (Access Point....in wireless parlance) that's far away and you only have for example 1 or 2 bars of signal at your location, you can then set up another AP at that location to rebroadcast the wifi and use the other AP's signal as a backhaul. i.e. without having the second AP connected to any wires.
Look up "WDS" or wireless repeating.
