Efflammation
Efflammation (pronounced /ɛfləˈmeɪʃən/) refers to proflation of fire—that is, to the discharge of flame from the mouth or nostrils or analogous orifices. It is frequently known in nontechnical contexts as "fire-breathing", though it has little connection with literal breathing, in the sense of respiration; certainly "fire-breathing" life forms can't extract oxygen from fire, since fire itself consumes oxygen. A life form capable of efflammation is said to be efflammant. (Sometimes the noun "efflammator" is used to refer to an efflammant being, but this word remains relatively rare.)
Because of the heat produced by efflammation, many life forms capable of the process also have a strong heat tolerance, being resistant or immune to temperatures that would burn or incinerate most ordinary organisms. If not the entire body, at least the throat and mouth lining, the parts most exposed to the heat, are likely to have this salamandrine property; indeed, it may happen that such an efflammatory entity burns up in a fire and only these parts remain, a disembodied and singed but intact trachea while the rest of the creature is turned to coal and ash. Even this is not necessarily the case, however; creatures do exist that project the brunt of the flames far enough from their bodies that they need no more heat tolerance than a creature without such abilities, and that are just as vulnerable as such beings to high temperatures.
Mechanisms
Efflammation can be produced by a variety of different mechanisms, all with similar end effects. Some efflammatory creatures simply produce magical fire with no fuel or physical basis for the flames. Others, however, make use of various combustibles and comburents. Many efflammatory creatures vomit forth flagrable gases; more rarely the substances involved are in liquid or pulverous form. These accendible substances are then either ignited with a spark (perhaps produced through friction between specialized organs in the creature's mouth or throat), or simply heated until they combust. Other efflamatory creatures transmute the air or other surrounding materials into the necessary inflammables.
By something similar to this last method, humans and other normally nonefflammatory beings can mimic fire-breathing, to a limited extent, by taking into their mouths and then spitting out ignitable substances such as mineral oil or cornstarch, lighting on fire the exputory aerosol. This effect is often used in carnivals and circuses, and is known sometimes as "fire-spitting", and perhaps formerly as "figgum", but most commonly, like efflammation, as "fire-breathing". Because this is done with the aid of outside tools and materials rather than as an innate product of the performer's body, however, this is not considered to be true efflammation, any more than blowing out cigar smoke composes true effumation, or taking up a mouthful of water and spitting it out sipation. (Needless to say, this fire-spitting is dangerous to the inexperienced, and carries serious risk of injury if not done correctly.)
Variations
While the usual vision of efflammation is that of great gouts of orange flame, not all efflammation necessarily has precisely this appearance. Efflammational fire can also take the form of narrow jet-like blazes, or of compact spherical fireballs. The color can also vary; the orange of typical woodfires is most common, but the flames can also be green, blue, or virtually any color, not excluding (with the aid of magic or of physics different than those of Xi) such dull hues as black, brown, or grey. Aside from the cosmetic aspects, the temperatures of the fires may also vary; some efflammations are more for show than for actual damage and may be slightly warm but not enough to burn flesh, while others, in extreme cases, can reach temperatures comparable to those at the surfaces of stars. Many efflammatory beings have control over the temperatures (and/or other characteristics) of their proflations, perhaps capable of choosing whether to vomit out a searing sunfire or a relatively tepid flame.