Also, one who is a flirt, one who has sex or intimate relations with many is defined as a player. This is an extension of adrianthomas's 2nd point, a player is someone who plays people, to make the victim think that the player is in love with them, then the player manipulates the victim to get what he/she wants (usually sex), and dumps them later.
The played are often left with a broken heart. Cruel isn't it?