Extreme card manipulations -- or "XCMs" -- are demonstrations of dexterity and skill with cards. This is not your normal shuffling, fanning, spreading, and accidentally dropping of cards, but much more difficult manipulations. They may include (among other things):
Although XCM practitioners would have you believe that they are "hand lordz" with "mad skilz" or other qualities lacking a final "s," the truth is that their demonstrations are nothing more than magic tricks. A simple stationery-store brad through a hole drilled through the corner of a deck of cards makes fanning a breeze. It's easy to cut a deck with one hand when the two halves are bound together with Scotch tape. Anyone can perfectly spread or waterfall a deck of cards tied together with a bit of string through the cards' centers. Want to throw a card and have it come back to you? All you need is a steel card and a serious magnet.
As an extra safety net, many XCM practitioners also attach their deck of cards to their sleeve with a bit of elastic, so that if they drop something, it just bounces back up and looks like another demonstration of skill.
By the way, many people ask why extreme card manipulations are referred to as "XCM" instead of "ECM". The answer is that these practitioners have spent so much time honing their craft that they have neglected their spelling studies.