Demons
In medieval magic, the term sigil was commonly used to refer to occult signs which represented various angels and demons which the practitioner might summon. The magical training books called grimoires often listed pages of such sigils. A particularly well-known list is in The Lesser Key of Solomon, in which the sigils of the 72 princes of the hierarchy of hell are given for the magician's use. Such sigils were considered to be the equivalent of the true name of the spirit and thus granted the magician a measure of control over the beings.
While some people fear demons, or attempt to exorcise them, others willfully attempt to summon them for knowledge, assistance, or power. The ceremonial magician usually consults a grimoire, which gives the names and abilities of demons as well as detailed instructions for conjuring and controlling them. Grimoires are not limited to demons – some give the names of angels or spirits. The use of ceremonial magic to call demons is also known as goetia, the name taken from a section in the famous grimoire known as the Lesser Key of Solomon.