Woolie posted a link to what it kind of is (He actually posted a link to a DAS. A MOP (Machine Orbital Polisher is a different tool)What's a maguires mop? should I have one?
Should you have a MOP? I would say no, you should not if you don't know what they are.
If they are not used correctly, with the right products, they are a very quick way to have to give a few hundred quid to your local paint repair shop to fix the damage that they can create in the wrong hands/with wrong technique.
A DAS (as linked to) is much less dangerous, but can still create a goodly amount of paint damage for a determined bodger. They (the DAS) are also much slower then a MOP and can take forever with some paints to get a result. Due to the vibration, they also can for some people be very uncomfortable to use (they give me the 'white finger' effect after only about 5 minutes I much prefer the MOPs)
(can you tell I am not a DAS fan )