When there is a division (vote) in the House of Commons, MPs leave their seats and walk into whichever division lobby corresponds to the way they want to vote. By tradition, Aye is a 'yes' vote in divisions in the House of Commons. If MPs want to vote yes, they go into the Aye Lobby. The Aye Lobby is the room on the right of the Speaker, behind the Government benches. If they want to vote no, they go into the No Lobby. The No Lobby is the room on the left of the Speaker, behind the Opposition benches. In the House of Lords there is a Content Lobby and a Not Content Lobby.
Further information on this subject can be found from the following links.
About Parliament: divisions
Related glossary term: Content and Not Content Lobbies
House of Commons Information Office factsheet: Divisions