The following is lifted (with the usual cautions) from urbandictionary.com. The grammar has been corrected as well.
Player: A male who is skilled at manipulating ("playing") others, and especially at seducing women by pretending to care about them, when in reality he is 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.