A club's 25-man roster is its full roster of active Major League players. Typically, a club will have some combination of 12 position players and 13 pitchers or 12 pitchers and 13 position players. Players on the 25-man roster (or the Major League disabled list) accrue Major League service time. All players on the 25-man roster must also be on the 40-man roster.
In the case of doubleheaders, clubs are allowed to recall one additional player to serve as the 26th member of the active Major League roster only for the day of said doubleheader. That player is returned to the Minor Leagues following the completion of the doubleheader.