Transfer is the way that the game (and the immortals, if they see fit) magically transports you from one place to another. Not to be confused with the transport spell (they are both often abbreviated to 'trans'), transfers are very common elements in mob and room progs. Most times that you move somewhere not of your own volition, the game has transferred you. When immortals transfer you somewhere, you get a message to the effect.
Solving some mazes involves finding the room that will trans you to another in order to progress through it, known as a trans room.