A male who is skilled at manipulating ("playing") others, and especially at seducing women by pretending to care about them, when in reality they are only interested in sex. Possibly derived from the phrases "play him for a fool", or "play him like a violin". The term was popularized by hip-hop culture, but was commonly recognized among urban American blacks by the 1970s.
A certain class of low-rent, slack-jawed fuckups has decided that backstabbing and misogyny are totally radical, so the word is sometimes used as a compliment or term of endearment between male friends, as in the greeting "what's up, player?".
Gina thought she had found the love of her life when she met Sean, but after she found out he had slept with three of her best friends, she realized that he was nothing but a player.