As one person tosses the coin in the air, the other person calls either heads or tails,” Grammarist explains. “Heads refers to the side of the coin with a person's head on it. Tails refers to the opposite side, not because there is a tail on it, but because it is the opposite of heads.”. Learn the terms for the parts of a coin, including obverse and reverse, and examples of coin finishes. The back side (“tails”) of a coin. Edge. So, when trying to determine who goes first, or who gets to choose a film, if the person calls out 'heads' and the heads side of the coin lands face.