Jann (singular: Janni) are the weakest of the various genie races to be found in the realms of Dungeons & Dragons. Unlike their mighty kinsfolk - the Dao, Djinn, Efreet and Marid, who are elemental creatures bound to a singular element, the jann are genies who combine multiple elements. This weakens them and binds them to the Material Plane, compelling them to exist on that plane rather than dwelling amongst their kinsfolk. In Advanced Dungeons & Dragons, jann can only spend 48 hours on the Elemental Planes before their life starts to seep away from them, compelling them to return to the Material Plane for another 48 hours in order to rejuvenate themselves.
These genies look like statuesque humans or half-elves with handsome, noble features. Their flesh is the color of sand and earth, and (unlike djinn) they may pass unnoticed among mere mortals without attracting undue attention. Their eyes may be blue, green, brown, black, or something in between, but they often seem to flash like hot, colored sparks, lively and energetic. They are most commonly found in the wild places of the world, typically in desert regions because, y'know, genies, Arabia, do we need to draw you a picture? Culturally, jann draw a lot from the stereotypical Arabian medieval nomad tribe, and frankly can easily be mistaken for just ordinary nomad tribes, until they display their magical powers.
These creatures travel in clans of 1d20 +10 individuals, each ruled by a sheikh with the aid of one or two advisors. Exceptionally powerful sheiks are given the title of amir, and in times of need they gather and command large forces of jann (and sometimes allied humans). The jann tribes travel with herds of camels, goats, and sheep between good grasslands and oases. As a people, they are the emblem of the virtues of the desert. They are strong, brave, and valiant. They are proud and brook no insult or impropriety, and see that injuries are repaid in kind. By the same token, they are hospitable to travelers and strangers, and treat them with honor and respect when they are among them, expecting the same treatment in return.
On the move, jann live in large, brightly-colored tents with their families. Male and female jann are treated equally, and a successful male or female may have a number of spouses. Traditionally a married male remains within (or at least near) his family's tent. A married female lives with her first spouse's family until she marries again, at which time a neutral location for her tent is chosen. Whenever a family outgrows a single tent, children move into their own quarters.
Jann also maintain permanent settlements in hidden oases, windswept holy sites, and deserted cities. Tents are common in such permanent locations, but the jann also build elegant, sweeping structures for communal use. Such structures might include a mosque, bathhouse (with quarters for visiting marids), smokehouse (with similar quarters so that efreet are comfortable), and occasionally an audience chamber for the jann's amirs.
Their relationship with the other genies is, of course, shaped by the general personalities of those genies. Jann are on excellent terms with djinn, and in an emergency the jann will send a messenger to the Elemental Plane of Air to request reinforcements. The jann tolerate efreeti, who tend to be foul-tempered and overbearing, taking advantage of any hospitality offered while offering little in return. Similarly, jann tolerate dao, but often with a thinly veiled hostility, because jann are sometimes captives in the dao's native plane. The marids are treated as the royalty they consider themselves to be, but their visits to the waterstricken deserts are, understandably, infrequent.
Jann first appeared alongside the Dao and the Marid in the article "Featured Creatures" of Dragon Magazine #66, for Advanced Dungeons & Dragons 1st edition. They were updated to 2nd edition in the Monstrous Compendium Volume 2, before appearing alongside the other four genies in the Monstrous Manual. Like their kinsfolk, they benefited from Al-Qadim; their largest amount of fluff ever was to be found in the Land of Fate boxed set, and their culture also fleshed out in the Genie-centric splatbook "Secrets of the Lamp".
In Dungeons & Dragons 3rd Edition, jann somehow lucked out into appearing in the Monster Manual, alongside the djinn and the efreet. They haven't appeared since, possibly because they are, fluffwise, the weakest and least interesting of the genies, and probably because their trappings as "generic Arabian nomads with magical powers" A: can be filled by just taking your not!Arabian nomads and making them full of sorcerers, and B: have some rather /pol/ connotations in this day and age.