A pell is like a punching bag except instead of punching you hit it with melee weapons like swords and instead of a bag it's log. In my case a roughly 8" diameter, ~3' long 12-15 pound Hickory log suspended by a cable.
You set it swinging and you cut on it as it comes and goes to work on your distance and timing or you can get a little closer and parry, block and side-step it so it doesn't knock your teeth out.
There are also smaller pells used to improve one's cutting precision and edge alignment. These are usually made of brass and sometimes incorporate a bell into the design.