Magic, as applied to sentient beings, is a form of energy linked to the soul. Users of magic draw upon the soul to perpetrate supernatural phenomena, such as projection of extranormal materials, transmutation of different forms of matter and energy into others, or manipulation of universal constants. It has been attributed at various times to the gods, to various supernatural entities or to extradimensional energies upon which we draw. The form that magic is projected in differs depending on the soul; it is theorised by the writings of Reichmann, Tezuka and Crowley, the composition, temperament and disposition of the soul affects the manifestation of magic. However, it is possible for someone to learn magic that is not innately theirs, though at lesser effectiveness and with careful study. Overall, this is what is referred to as magic in as far as it refers to sentient beings; what mundane people refer to as 'wizardry' or 'sorcery'.
Magic, as applied to other fields, is referring to a wide range of supernatural phenomena that are not under the purview of the manipulation of spiritual energy, such as the imbuing and creation of magical relics and the creation of potions with effects beyond the scope of mundane chemistry. Beyond the use of the term 'magic' to refer to the phenomena in reference to the use of spiritual energy by sentient beings, the word becomes vaguely defined and difficult to pinpoint. This point occurs in the writings of Crowley in particular, who argues that there is a distinction between the use of magical rituals such as circles and drawing from leylines and the use of innate magic to achieve the aim of cursing an opponent, due to the different mechanisms at work behind both forms of 'magic'.
In this respect, magic is a catch-all term that refers to the general field of supernatural phenomena accessible to those in the world beyond the mundane, as posited by Crowley and Tezuka.
In my opinion, magic is using supernatural energy to do things that mundane people either can't normally do or would take much more effort to do, such as flying or shooting thunderbolts. Tezuka argues that magic is based on the person's personality and their soul, and this explains why so many people have such different magical powers; because people are so different, people have many different specialties of magic. They can also learn other magic spells and rituals, but that is harder to do than if you already have it innately.
It also refers to the other weird things supernatural people do, such as make potions, do magical rituals, and create relics and artifacts. However, those don't seem to be the same as doing magic with magic you already have. Mundane people might just call it magic because a potion that gives you luck is just as weird as healing people with lightning bolts.
So, magic is a word people use to refer to anything supernatural in general.
I believe magic is the term one uses to refer to the use of spiritual energy to create extranormal events. It has different forms and so cannot be defined by any one manifestation of magic; it can be as projection of objects, manipulation of existing materials or transmutation of one form into another. Some writers, such as Reichmann, theorise that magic is defined by one's disposition and unique nature, explaining the inherent rarity of mages who are innate experts at the same form of magic.
Magic, however, need not only be based on one's innate abilities, as one can learn other forms of magic with intense study, at the cost of potency. The term is also a catch-all used to refer to other supernatural fields, such as potionmaking, artificing and divination. This use of the term can be said to be more the result of mundane confusion over the distinction between magic as the result of spiritual energy and the effects of potions and magical artifacts; while similar, they cannot be said to be the same thing.
As one sees it, magic should only be used to refer to the specific use of the energy of one's soul in the initiation of supernatural phenomena, with reference to other fields only as convenience in the absence of a better term.