a type of door in the entrance of a large building, which goes around and around as people go through it
used to say that the people involved in a situation, organization etc change often:
The park director position has been a revolving door for seven appointees.
used to say that people return to a situation, position etc often, but usually for a different reason:
This could mean that we end up with a revolving door Congress, in which former members return as lobbyists.