Magic is a performing art that entertains an audience by creating illusions of impossible feats, using purely natural means. These feats are called magic tricks, effects or illusions.
An artist who performs magic is called a magician. Magicians (or magi) are also referred to by names reflecting the type of magical effects they typically perform, such as prestidigitators, conjurors, illusionists, mentalists, ventriloquists, and escape artists, etc.

History
There is much discussion among magicians as to how a given effect is to be categorized, and disagreement as to what categories actually exist -- for instance, some magicians consider "penetrations" to be a separate category, while others consider penetrations a form of restoration or teleportation. It is generally agreed that there are very few different types of effect. While many authors such as Fitzkee, Tarbell, S.H. Sharpe and others have disagreed, it has often been said that there are only seven types of illusion (perhaps because it is considered a magic number).
Many magical routines use combinations of effects. For example, in the famous 'cups and balls' a magician may use vanishes, productions, penetrations, teleportations and transformations all as part of the one presentation.

Production The magician produces something from nothing—a rabbit from an empty hat, a fan of cards from thin air, a shower of coins from an empty bucket, or the magician themselves, appearing in a puff of smoke on an empty stage -- all of these effects are productions.
Vanishing The magician makes something disappear—a coin, a cage of doves, milk from a newspaper, an assistant from a cabinet, or even the Statue of Liberty. A vanish, being the reverse of a production, may use a similar technique, in reverse.
Transformation The magician transforms something from one state into another—a silk handkerchief changes colour, a lady turns into a tiger, an indifferent card changes to the spectator's chosen card. A transformation can be seen as a combination of a vanish and a production.
Restoration The magician destroys an object, then restores it back to its original state—a rope is cut, a newspaper is torn, a woman is sawn in half, a borrowed watch is smashed to pieces—then they are all restored to their original state.
Teleportation The magician causes something to move from one place to another—a borrowed ring is found inside a ball of wool, a canary inside a light bulb, an assistant from a cabinet to the back of the theatre. When two objects exchange places, it is called a transposition: a simultaneous, double teleportation.
Levitation The magician defies gravity, either by making something float in the air, or with the aid of another object (suspension)—a silver ball floats around a cloth, an assistant floats in mid-air, another is suspended from a broom, a scarf dances in a sealed bottle, the magician hovers a few inches off the floor. There are many popular ways to create this illusion of the magician himself being levitated, such as the Balducci levitation, the King Rising, Criss Angel's stool levitations, the Andruzzi levitations, and the eight gravity.
Penetration The magician makes a solid object pass through another—a set of steel rings link and unlink, a candle penetrates an arm, swords pass through an assistant in a basket, a saltshaker penetrates the table-top, a man walks through a mirror. Sometimes referred to as 'solid-through-solid'.
Prediction The magician predicts the choice of a spectator, or the outcome of an event under seemingly impossible circumstances—a newspaper headline is predicted, the total amount of loose change in the spectator's pocket, a picture drawn on a slate. Prediction forms the basis for most 'pick-a-card' tricks, where a random card is chosen, then revealed to be known by the performer. Categories of effects
The purpose of a magic trick is to amuse and create a feeling of wonder; the audience is generally aware that the magic is performed using trickery, and derives enjoyment from the magician's skill and cunning. Traditionally, magicians refuse to reveal the secrets to the audience. The reasons include:
Membership in professional magicians' organizations often requires a solemn commitment to the "Magician's Oath" never to reveal the secrets of magic to non-magicians.
The Magician's Oath (though it may vary, 'The Oath' takes the following, or similar form):

"As a magician I promise never to reveal the secret of any illusion to a non-magician, unless that one swears to uphold the Magician's Oath in turn. I promise never to perform any illusion for any non-magician without first practicing the effect until I can perform it well enough to maintain the illusion of magic."
Once sworn to The Oath, one is considered a magician, and is expected to live up to this promise. A magician who reveals a secret, either purposely or through insufficient practice, may typically find oneself without any magicians willing to teach one any more secrets.
However, it is considered permissible to reveal secrets to individuals who are determined to learn magic and become magicians. It is typically a sequential process of increasingly valuable and lesser known secrets. The secrets of almost all magical effects are available to the public through numerous books and magazines devoted to magic, available from the specialised magic trade. There are also web sites which offer videos, DVDs and instructional materials. In this sense, there are very few classical illusions left unrevealed, however this does not appear to have diminished the appeal of performances. In addition, magic is a living art, and new illusions are devised with surprising regularity. Sometimes a 'new' illusion will be built on an illusion that is old enough to have become unfamiliar.
Some magicians have taken the controversial position that revealing the methods used in certain works of magic can enhance the appreciation of the audience for cleverness of magic. Penn and Teller frequently perform tricks using transparent props to reveal how it is done, for example, although they almost always include additional unexplained effects at the end that are made even more astonishing by the revealing props being used.
Often what seems to be a revelation of a magical secret is merely another form of misdirection. For instance, a magician may explain to an audience member that the linking rings "have a hole in them" and hand the volunteer two unlinked rings, which the volunteer finds to have become linked as soon as he handles them. At this point the magician may shove his arm through the ring ('the hole in the ring'), proclaiming: "See? Once you know that every ring has a hole, it's easy!"
See also: Intellectual rights to magic methods

Exposure is claimed to "kill" magic as an artform and transforms it into mere intellectual puzzles and riddles. It is argued that once the secret of a trick is revealed to a person, that one can no longer fully enjoy subsequent performances of that magic, as the amazement is missing. Sometimes the secret is so simple that the audience feels let down, and feels disappointed it was taken in so easily.
Keeping the secrets preserves the professional mystery of magicians who perform for money. Secrecy
The teaching of performance magic was once a secretive art. Professional magicians were unwilling to share knowledge with anyone outside the profession to prevent the laity from learning their secrets. This made it difficult for an interested apprentice to learn magic beyond the basics. Some organizations of magicians had strict rules against members discussing magic secrets with anyone but established magicians.
From the 1584 publication of Reginald Scot's Discoverie of Witchcraft until the end of the 19th century, only a few books were available for budding magicians to learn the craft. Books remain extremely useful today, and are still considered the best way for a student to learn magic. Videos and DVDs are a newer medium of tuition, which many inexperienced magicians rely on as a primary source of information; in reality, many of the methods found in this format are readily found in previously published books. However, they can serve useful as a visual demonstration.
The next step up is joining a magic club or workshop. Here magicians, both seasoned and novitiate, can work together and help one another for mutual improvement, to learn new techniques, to discuss all aspects of magic, to perform for each other — sharing advice, encouragement and criticism.
The world's largest magic organization is the International Brotherhood of Magicians. It publishes a monthly journal, The Linking Ring. The oldest organization is the Society of American Magicians, of which Houdini was a member; and in London, England, there is the Magic Circle which boasts the largest magic library in Europe. The Magic Castle in Hollywood is home to the Academy of Magical Arts.