Tel'aran'rhiod (tel-AYE-rahn-rhee-ODD) or the World of Dreams is a fictional reality where the reality is mutable, mentioned in the fictional world of Robert Jordan's fantasy series The Wheel of Time. The word itself is from the in-universe language known as the Old Tongue, literally meaning 'the unseen world'. In Tel'aran'rhiod dreamers are self-aware, and environments are malleable, depending on the awareness of the dreamers. Additionally, the perception of time in Tel'aran'rhiod is different from the awaking world.
Though normally accessible only through dreams, Tel'aran'rhiod is in fact a real place. Its geographical reality is dependent on the waking world, but its contents can be and are altered by the works of non-sleeping people. Those things which are sedentary in the waking world—buildings, furniture, mountains, forests—tend to stay put in the Dream, but things that move or see use—utensils, personal correspondence, clothes, even tent or wagon settlements—are much harder to find, and may disappear once discovered. All reality is mutable in Tel'aran'rhiod; those inside it can alter themselves and the world around them, including abilities such as instant wardrobe changes, the creation of scenery (or once, a horse), flight and levitation, instant travel across huge distances, and so forth. These tweaks are often subconscious, and it takes a certain amount of concentration to control or prevent them. Skilled Dreamwalkers, those who can enter Tel'aran'rhiod unaided, can also impose their creations upon other people, often with frightening and, if desired, lethal results. Injuries taken in Tel'aran'rhiod, including death, are reflected in the waking world. Wild animals and humans can enter Tel'aran'rhiod, while domesticated animals have lost this ability. Normal people occasionally visit Tel'aran'rhiod through their dreams, generally flitting in and out for a few seconds without ever realizing it. Most come to no harm, but rarely some are fatally injured and never wake up.
Despite its idiosyncrasies, Tel'aran'rhiod has proved a vital source of intelligence for the series' characters. Visits to allied settlements and enemy headquarters (specifically the Amyrlin's office in the White Tower) have yielded important intelligence, and Egwene, Nynaeve, Elayne and the Aiel Wise Ones use it to share news, formulate plans, and sometimes just to socialize.
The ability to enter Tel'aran'rhiod at will is known as Dreamwalking, and those who possess it are usually far more adept at manipulating the nature of the dream. The White Tower was under the impression that this was a skill that only those who could channel might possess, however the Wise Ones of the Aiel have members who are adept at Dreamwalking without the ability to touch the One Power, most notably Bair. A related talent, usually referred to simply as Dreaming, is the ability to have precognitive dreams, though they are often difficult to interpret. Currently, the most notable Dreamer in the Tower is Egwene al'Vere; the last one before her was Corianin Nedeal, almost 500 years ago. Two other experts in the dream are known to exist: the Forsaken Moghedien and Lanfear, though Lanfear's Dreamwalking capabilities are uncertain in her current form, known as Cyndane.
The White Tower has a number of ter'angreal that allow access to Tel'aran'rhiod, but some require channeling to function and create a strange, sickly feeling while being used. Their use is also limited by the fact that a channelers strength is drastically restricted while dreaming; while the ter'angreal require relatively small amounts of the One Power, even that much may be out of reach while in Tel'aran'rhiod. Most of the known ter'angreal with this ability are in the possession of the Salidar rebels or were stolen by the Black Ajah.
Wolfbrothers, like Dreamwalkers, can also enter Tel'aran'rhiod, as can all wolves. Tel'aran'rhiod is where wolves go when they die.
It is also possible to enter Tel'aran'rhiod "in the flesh," by Travelling there. This is considered an abomination by the Aiel, as those who enter in the flesh lose some unknown part of their humanity. Contrarily, those fully in Tel'aran'rhiod appear to experience a massive increase in control over the dream. The thought of opposing one who had entered in the flesh was enough even to frighten Moghedien, whose power in the Unseen World was greatest among the Forsaken. When Ishamael entered Tel'aran'rhiod in the flesh in The Dragon Reborn, he was capable of extraordinary feats, such as gravity manipulation and even unravelling reality.