In Irish mythology and folklore, a geis (/ˈɡɛʃ/; [ˈɟɛʃ]; plural geasa) is an idiosyncratic taboo, whether of obligation or prohibition, similar to being under a vow or spell. The Scottish Gaelic spelling "geas" is also common.
A geis can be compared with a curse or, paradoxically, a gift. If someone under a geis violates the associated taboo, the infractor will suffer dishonor or even death. On the other hand, the observing of one's geasa is believed to bring power. Often it is women who place geasa upon men. In some cases the woman turns out to be a goddess or other sovereignty figure.
The geis is often a key device in hero tales, such as that of Cúchulainn in Irish mythology. Traditionally, the doom of heroes comes about due to their violation of their geis, either by accident, or by having multiple geasa and then being placed in a position where they have no option but to violate one geis in order to maintain another. For instance, Cúchulainn has a geis to never eat dog meat, and he is also bound by a geis to eat any food offered to him by a woman. When a hag offers him dog meat, he has no way to emerge from the situation unscathed; this leads to his death.
GEAS (Grand Edinburgh Adventuring Society, also known as GEAS Roleplaying Society or Edinburgh University Roleplaying Society) is the roleplaying society of the University of Edinburgh. The society plays host annually to Conpulsion, Scotland's oldest, largestgaming convention.
GEAS was founded in 1978 with a stated goal of "[fostering] the cause of all roleplaying games." It gained a website in the early days of the Web (1993/1994), which by 1997 was reputedly "Europe's most popular roleplaying website", and accounted for almost half the web traffic of the University of Edinburgh. By the time the GEAS Village (as it was known then) closed, sometime in September 2001, it had been the largest independent roleplaying website in the world, primarily due to its use of then-cutting edge technology in combining graphics, archives of roleplaying material, and some of the world's first internet message boards.
In 1987, GEAS ran a convention titled Dungeon Aid to raise money for charity. The event proved very popular so became an annual fixture, renamed Big Con after a few years, then Conpulsion in 1995.