The significance of the title "The Player" in both Robert Altman's 1992 film and in Michael Tolkin's novel, from which the screenplay was adaped, lies in its use of a common term denoting one who is adept at manipulating processes, especially in the business world, for personal advantage.  "Players" are individuals who are active at networking and in the behind-the-scenes maneuvering that can often dictate the direction in which corporate or office policy moves.  The "protagonist" of "The Player" is Griffin Mill, a film company executive who works the system by which screenplays are purchased and turned into films, or buried in the piles of unproduced scripts that litter many Hollywood offices.  Mill is a successful producer, and the film, putting aside the issue of threatening letters from a disgruntled wannabe screenwriter who Mill murders, is about the machinations that are a common feature of that particular industry.  One of the more telling exchanges in the film involves a discussion between Mill and Larry Levy, another industry executive:

Levy: I'll be there right after my AA meeting.

Mill: Oh, Larry, I didn't realize you had a drinking problem.

Levy: Well, I don't really, but that's where all the deals are being made these days.

Griffin Mill is a "player";  so are many of the people he encounters in the course of a routine business day. Superficial displays of cordiality and affection mask a nasty, bitter process that is business-as-usual for the characters in Altman's film (which is far superior to the book).  Duplicity and back-stabbing is stock-in-trade for Mill and his colleagues and competitors.  The cynicism inherent in their character is intended as an indictment of the "Hollywood system."  In order to succeeded, one has to be a player.