Geasa is a Celtic metal band originating from Dublin, Ireland. The band combines traditional Celtic music with black metal to form Celtic black metal. They formed in 1994 and have been active since, releasing one demo album, one EP, and three full-length albums.

The band derived its name from geis (pl. Geasa), which in Irish mythology and folklore, is an idiosyncratic taboo, whether of obligation or prohibition, similar to being under a vow or spell. 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.

Source : www.wikipedia.org