Basically, fanning the clutch is where you hold the clutch lever in just far enough to allow a small amount of slippage, but still keep it engaged enough to be putting power to the wheels. This allows you to keep the engine revs in the meat of the power, even when you are otherwise going too slow in the gear you are in to be in the powerband. This works great for two-strokes, but it tends to destroys clutches in four-strokes (which don't generally need this type of abuse anyway).