Tel'aran'rhiod is the "World of Dreams". Most people enter it while dreaming, though only for a few moments at a time. Dreamwalkers can enter it at will. It resembles the real world, except for the absence of most of the people and other living beings.
Tel'aran'rhiod can be used to reach a particular person's dreams, but one must be careful not to be drawn too deeply into the dream, or give up their control of events to the dreamer.