From OpenStreetMap Wiki
|Marks free exit of a building/restricted area.|
|Used on these elements|
|Status: in use|
|Tools for this tag|
If you don't need a key to go out from a building or restricted area, you can mark this with exit=yes. This tagging has sense, if rules for exit are different from rules for entrance. Most common value is yes. There are also a few exit=emergency.