Jinn are introduced in several Ars Magica Supplements, such as RoP: Magic, The Cradle & The Crescent, and HoH: Societates. However, the definition of what a Jinn is, in ludic terms, has some problems.

The Cradle & The Crescent provides the most thorough definition, in Ch.4 "The Jinn." Unfortunately, that definition, and the other more brief descriptions that occur in other supplements, define Jinn as beings that are found in Islamic lands.

While this might function for Faerie Jinn, who are defined as having accepted or rejected Islam, it makes no sense for Magic Jinn, who are explicitly stated as showing "little interest in the affairs of mankind or the message of the Prophet." Why should one magic spirit be classed as a "Jinn" while another, otherwise identical spirit is not, simply because one is encountered in southern Iberia, and the other in northern Iberia?

The answer, of course, is that there is no good conceptual reason for this distinction to be drawn between spirits of magic. The root cause of this issue is the unfortunate decision to define Jinn as a ludic class, rather than just the name that one set of cultures gives to a certain type of being.

The way out of this conceptual mess is to re-define what Sihr is capable of summoning. Rather than summoning anything described as a "Jinn," Sihr can summon any spiritual being that is neither angel nor demon, and which did not originate as a mortal being (i.e. not a ghost, or ascended magus, or any other variation of spirit that once was not a spirit).

Faeries are spiritual beings of this sort only if they have the Intangible Flesh Flaw. This does change the rules about "animal" Jinn somewhat, but it is still possible to have a Jinn that can assume animal form, for example, or even one that can assume both a human and an animal form.

Infernal spirits of this sort will tend to be Faerie or Magic spirits that have been corrupted by the Infernal, such that they now have Infernal Might. Infernal ghosts are not this sort of being, nor are demons. Demons could, however, pretend to be this sort of being. The difference would be that Sihr is not truly summoning the demon; the demon is appearing because it chooses to do so.

By re-defining the categories of being that Sihr can affect, and discarding the culture-specific appelate "Jinn," most of the difficulties related to "what is a Jinn?" are resolved.

The answer, then, to the question "What is a Jinn?", is that a Jinn can be anything that someone from an applicable culture calls a Jinn, regardless of its nature. Faeries that turn into animals, for example, might be called Jinn, but they are not summonable by Sihr unless they are inherently spiritual - having Intangible Flesh.

This change of definition leaves other Summoning Arts unaffected, except perhaps that some things that are not spiritual in nature could still be called "Jinn" and a summoner could think of herself as summoning "Jinn."