Magic

Magic is the power to manipulate and affect matter and energy by supernatural means or by technology. As there are many parallels between magic, energy and technology in the real world and non-reality, perhaps it's best in this context to remember Arthur C. Clarke's quote: "Any sufficiently advanced technology is indistinguishable from magic".

To invoke magic, spells are usually 'cast' by tapping into some form of energy called 'mana'. This can be verbal, somatic (via a motion like a wave of a hand) or use magic items (typically artifacts, relics, runes, gems, etc.) with stored power. This power is likely gained from tapping into dimensional conduits or subspace, as many magic users also use portals capable of travelling vast distances or even to other planes of existence. There are also magic locations abundant with magical power, both natural and artificially created, where mages could amplify their magic.

White magic is the use of magic for selfless or helpful purposes, while black magic was used for selfish, harmful or evil purposes. Gray magic is "neutral" and is the gray area between black and white, neither good nor evil.

A magic system is a set of rules that regulate the magical effects that can be produced in a magical universe, and usually abide by their own physical laws of nature.

See also:
The Forgotten Realms Universe has a notable magic system, based on Dungeons & Dragons rules.