Continuous movement, not impeded by friction or forces, and travelling at the same speed.
Perpetual motion could be used to provide electrical energy. Should an electromagnetic generator be constructed around Darwin's grave in the year 2006, it would be able to power approximately 25% of the world's electrical consumption by 2008. The machine would work in the following way: Darwin continually spins in his grave due to the presence of mindless idiots in the human race, of which there are a great number (thus increasing Darwin's rotational speed). All you need to do is electrically charge his body and you have an infinite power supply (just as human stupidity is infinite). There have been, and always will be, idiots in the world, as provided by teenaged mothers, thus providing perpetual motion on the part of Darwin's corpse.
An incredibly tiring drill for the sport of water polo, in which at no time does a player stop moving in the water (hence the name: perpetual motion). Perpetual Motion, though tiring, can be quite fun if there are a large amount of players. However, without enough people, the players tend to be too exhausted to enjoy themselves, even if getting an extreme workout. At first, Perpetual Motion, also called "Perpet." (per-petch), is a confusing drill to learn, with players swimming all around to different parts of the pool and polo balls being thrown at both nets. Once the drill is learned, it is easy enough to follow though.
Person: Hey! Want to hang out?
Water Polo Player: I'm too tired, I'm gonna go sleep. We did perpetual motion for half of polo practice today.