The Federal Open Market Committee, or FOMC, is the Fed's monetary policy committee. It meets eight times a year in Washington (the schedule is on the Fed's Web site) to set the fed funds rate.
Announcements of changes in monetary policy are at about 2:15 p.m. Eastern Time (on the second day if it's a two-day meeting), and the minutes of the meetings are released within a few days of having been approved by the committee at its subsequent meeting.
The FOMC has 12 voting members and five alternates. The seven Fed governors always vote, as does the president of the New York Fed. The other 11 District Fed presidents vote on a rotating schedule.
Alternates vote only if a District Fed president can't make the meeting. The first vice president of the New York Fed is the New York Fed president's alternate. The Chicago and Cleveland Fed presidents alternate for each other. And the other District Fed presidents are alternates the year before they vote. For example, if the Philly Fed president is absent, the Richmond Fed president votes instead.