From BR Bullpen

A trade occurs when two teams exchange players, future considerations or a player to be named later, money, draft picks or some combination thereof. In the major leagues, trades cannot be made after July 31, the trading deadline, unless the player(s) involved have cleared waivers. Players traded after August 31 are not eligible for the team's post-season roster. During the period of July 29-31, some teams out of contention trade their marquee players or players who are signed to large contracts for prospects or less expensive players.