Found art is a creative concept that dictates that whatever you see or discover can be called "art." This includes, but is not limited to, abandoned buildings, your neighbor's trash, scraps of paper, old newspapers, notes left on your car, or photographed phrases wiped into the dust on the back of a car.
Found art has its roots in the surrealism movement of the 1920s and 1930s and as such, it is among the favorite topics of the USENET newsgroup talk.bizarre.
A good example of found art would be someone's elaborately-penned shopping list that flutters into your hands as you sit on a park bench on a windy day, or a toilet you find in an alley somewhere, which you could take home, sterilize, and paint in an array of beautiful colors.
The movement was also quite popular with the Beatnik generation, but was all but dead to most people by the 1980s. It resurfaced in the 1990s, and many websites sprang up dedicated to the subject and its exhibition.
There are no actual artists within the found art movement, unless you count everyone who still has their eyesight intact. In almost all cases, exhibits were not originally intended as art and therefore can take on a bevy of meaning, leaving the interpretation of the piece in the eye of the beholder. It is one of the most bizarre, pleasing and ultimately original forms of modern art still being produced, and given the tenets of the definition, it's unlikely to go away anytime soon.
Perhaps one of the strangest instances of found art to come about in recent years is the dead rat game. However, I've never known anyone who has actually played it or witnessed it being played.