Relative exits are exits that are relative to the direction you're currently facing. They are: forward, right, backwards, left, forward-left, forward-right, backward-right, and backward-left.
Often, if a place uses relative exits, you won't be able to use the normal type of exit--north, south, east, west--there. The exception is real estate (where you see relative exits, but can use both).
You can generally use this type of exit even if the room you're in uses the normal type of exits, going "backwards" to go back to the room you just came from, and so on.
You can (usually) see which direction you're facing with the "facing" command.
You can change the direction you're facing with "turn":
turn <around, [half] right, [half] left, rt, lt>
The direction you're facing also changes when you move any direction except forwards.
The following things use this type of exit: