"Coin flipping, coin tossing, or heads or tails is the practice of throwing a coin in the air and checking which side is showing when it lands, in order to choose between two alternatives, heads or tails, sometimes used to resolve a dispute between two parties. It is a form of sortition which inherently has two possible outcomes. The party who calls the side that is facing up when the coin lands wins." (Wikipedia)

New: I added a simple scoreboard that can be useful in case you are using the Coin Flip to decide the first team/player in a match.