This time of year we hear the media and General Managers from all 30 MLB teams use a lot of different terms. One of those terms is the 40 man roster, so naturally a lot of us not in the know are left wondering what that means exactly.

For major league baseball teams we are really talking about two separate rosters. There is the active roster which covers the 25 players who play the games day in and out. These are the 25 players that may take the field for any game. Generally speaking these are the only players that travel with the team on road trips.

Now we have the 40 man roster of the expanded roster. This roster covers all 25 members of the active roster, plus all players on the 15 day disabled list, plus any player on optional assignment in the Minor Leagues.

Now players on one of these rosters or not have different rights. For example any player not on the 40 man roster as of November 20th may be eligible for the Rule 5 draft.

After September 1st the MLB allows its clubs to play with expanded rosters and then any player on the 40 man roster may play at the big league level. Most often these players are labeled September Call Ups as this is typically after the minor league seasons have ended.

After the Non Waiver trade deadline, which is usually the first of August, any player of the 40 man roster must clear waivers before he can be dealt to another team.