Magic: the Gathering is a game, a form of competitive activity played according to certain rules.
A game is also single portion of play forming a scoring unit in a match between (at least) two players. While you have full control of the selection of your own cards, your deck never exists in a vacuum. One half of a game of Magic is a constant, and the other is a variable that changes with every opponent.
An object is “outside the game” if it isn’t in any of the game’s zones.
From the Comprehensive Rules (Amonkhet (April 28, 2017))
- 100. General
- 100.1. These Magic rules apply to any Magic game with two or more players, including two-player games and multiplayer games.
- 100.1a A two-player game is a game that begins with only two players.
- 100.1b A multiplayer game is a game that begins with more than two players. See section 8, “Multiplayer Rules.”
- 100.2. To play, each player needs his or her own deck of traditional Magic cards, small items to represent any tokens and counters, and some way to clearly track life totals.
- 100.2a In constructed play (a way of playing in which each player creates his or her own deck ahead of time), each deck must contain at least sixty cards. A constructed deck may contain any number of basic land cards and no more than four of any card with a particular English name other than basic land cards.
- 100.2b In limited play (a way of playing in which each player gets the same quantity of unopened Magic product such as booster packs and creates his or her own deck using only this product and basic land cards), each deck must contain at least forty cards. A limited deck may contain as many duplicates of a card as are included with the product.
- 100.3. Some casual variants require additional items, such as specially designated cards, nontraditional Magic cards, and dice. See section 9, “Casual Variants.”
- 100.4. Each player may also have a sideboard, which is a group of additional cards the player may use to modify his or her deck between games of a match.
- 100.4a In constructed play, a sideboard may contain no more than fifteen cards. The four-card limit (see rule 100.2a) applies to the combined deck and sideboard.
- 100.4b In limited play involving individual players, all cards in a player’s card pool not included in his or her deck are in that player’s sideboard.
- 100.4c In limited play involving the Two-Headed Giant multiplayer variant, all cards in a team’s card pool but not in either player’s deck are in that team’s sideboard.
- 100.4d In limited play involving other multiplayer team variants, each card in a team’s card pool but not in any player’s deck is assigned to the sideboard of one of those players. Each player has his or her own sideboard; cards may not be transferred between players.
- 100.5. There is no maximum deck size.
- 100.6. Most Magic tournaments (organized play activities where players compete against other players to win prizes) have additional rules covered in the Magic: The Gathering Tournament Rules (found at WPN.Wizards.com/en/resources/rules-documents). These rules may limit the use of some cards, including barring all cards from some older sets.
- 100.6a Tournaments usually consist of a series of matches. A two-player match usually involves playing until one player has won two games. A multiplayer match usually consists of only one game.
- 100.6b Players can use the Magic Store & Event Locator at Wizards.com/Locator to find tournaments in their area.