Poles are the magnets in the rotor. 2 pole motor means 2 magnets,4 pole means 4 magnets. Obviously the more magnets the greater the magnetic pull/resistance when the rotor rotates inside the stator. 4 pole motors were basically designed for your 4x4 short course trucks so you don't have to use the large 550 size can which is heavier and designed for a 1/8th size vehicle. So you get 550 power in a 540 sized motor making them perfect for 1/10 4x4 sc. Most all other 1/10 size vehicles will use 540 size 2 pole motors. It's a brief explanation but it should help.