Magic
The Definition of Magic
In a universe where super-human abilities are well documented, it is difficult to distinguish "magic" from the non-magical ability to fly, project thoughts, or bend steel with bare hands. The fundamental difference, however, is that scientists have explained "powers" and have never explained "magic". For example, the gene that causes psychic powers has been identified, the quantum tunnelling that enables telepathy can be detected and measured, and machines can be created that reproduce those effects. Similarly, when a super-human flies by controlling gravitons, those gravitons can be measured, the controlling impulses in the brain can be detected, and machines can mimic the mechanism.
In short, there is always a measurable and reproducible causal link for any non-magical phenomenon. Magic, however, defies scientific investigation. It has no known physiological basis, there is no measurable energy exchange, and no detectable link between cause and effect. No machine has ever been created which can "use" magic.
Simply speaking, magic makes happen things which otherwise should not have happened. Thus it involves a manipulation of probability at a quantum level, but how it does that is inexplicable.
Scientists who have studied magic are roughly divided into two camps when it comes to a definition:
(a) Magic is simply a science that is not yet understood (this was the definition favoured by Q of Strikeforce and other noted scientists).
(b) Magic is a phenomenon that inherently can not be understood (this was the definition favoured by Centurion of Strikeforce and others).
It's interesting to note that the definition favoured by most magic users, including the Supreme Sorceress of Earth, runs along the lines of "I don't know what it is but I know it when I see it".
For practical purposes, this latter definition seems to be the most useful.
The Source of Magic
All authorities agree that "native" magic (that is, magic practiced by inhabitants of our universe) taps directly into the pure essence of the universe's consciousness. How that happens remains unknown. There are, however, non-native beings who draw magic from alternative sources. Foremost among these are demons (or, more correctly, demons' avatars in this dimension), which can tap the power of their home universes while inhabiting ours.
The Mechanism of Magic
In its simplest form, magic consists of a spoken sound, usually accompanied by a gesture. This would be a "spell". A specific combination of sound and gesture will produce a specific effect, for example the Atlantean verb will always produce a defensive shield. Thus spells can be written down and taught. Obviously the power is not inherent in the word alone, otherwise anybody could say the word (or a machine could play a recording of it) and have the same effect, and this is patently not the case.
In addition to the word and gesture, the magic user has to visualise the effect he wants. This is the "secret" ingredient of magic. In theory, anybody could be taught a magic word, or learn it from a spell book, but the ability to perform correct visualisations is an ability that very few people have ever mastered. Some magicians study for decades before achieving this ability; others appear to have a natural affinity. (Astra, for example, was instinctively able to cast spells as a teenager with no formal magical training—not always with desirable results.)
Many magicians concentrate on "themed" magic, for example only fire magic or only creature summoning. For various reasons (usually psychological, sometimes self-imposed), they are more adept at visualising those effects. For example, it is no coincidence that the terrorist called Hellfire specialised in fire magic after suffering horrific burns in a house fire. In addition, most magicians will have a very small number of spells that they can cast due to the intense practice required to perform different visualisations.
There are other forms of magic beyond simple spells. Ritual magic is a more complex form that requires greater time, the gathering of esoteric ingredients, symbolism, astrological conjunctions, and other paraphernalia. However it seems that all these preparations are simply a way of getting the magician into "the right frame of mind", or in other words to aid the visualisation of the magical effect. Thus a ritual might therefore enable more powerful magical effects or it might simply be a crutch for a weak magician to perform simple magic.
Most spells are written (and vocalised) in ancient languages: Atlantean is the most common because the Atlanteans were the first to study magic in depth and it is their work which has been passed down through the ages. Spells can also be found in Latin, many Chinese dialects, and other ancient languages. There is no need to actually understand the language of the spell; it is sufficient to pronounce it correctly while remaining ignorant of the meaning. It is interesting to note, however, that the most powerful magicians have been multi-lingual and naturally adept at picking up new languages.
Atlanteans
Despite appearances, there is no explicit link between Atlantean genes and magical ability. The high number of magic users who have claimed Atlantean ancestry appears to be due more to social factors than genetic ones, and the use of the Atlantean language to cast spells is due to historical factors as mentioned above.