T.1.1- The list of valid spell types is: instant, sorcery, artifact, artifact creature, creature, enchantment. [CompRules 1999/04/23]
T.1.2- The list of valid ability types is: activated ability (see Rule A.2), delayed ability (see Rule A.5), mana ability (see Rule A.6), static ability (see Rule A.3), and triggered ability (see Rule A.4). [CompRules 1999/04/23]
T.1.3- Artifact spells (and artifact creature spells), sorcery spells, creature spells, and enchantment spells can only be played during your main phase and only when the stack (see Rule T.2) is empty. [CompRules 1999/04/23]
T.1.4- Instants may be used on either player's turn during the Upkeep Step, Draw Step, Main Phase, End of Turn Step, and all steps during the Combat Phase. They can also sometimes be played during the Cleanup Step. They may be played on an empty stack (see Rule T.2) or on a stack which already has spells and abilities on it. [CompRules 1999/04/23]
T.1.5- The ability of a permanent with an activation cost is played whenever you could play an instant unless otherwise stated on the card. The only exception is that any activated ability which generates mana is played as a mana ability. [CompRules 1999/04/23]
T.1.6- An "event" is anything that happens in a game. [CompRules 1999/04/23] The term is usually used to describe an atomic action in the game, such as announcing a spell or ability, declaring attackers or blockers, or the resolution of a spell or ability. [D'Angelo 1999/05/01] A spell or ability may have multiple events in its resolution. [CompRules 1999/04/23] Something which appears as a single event to one thing may appear as multiple events to another. For example, whenever you declare attackers there are a number of separate events within the declaring attackers event. [CompRules 1999/11/01]
T.1.Ruling.1- The timing rules do not distinguish between spells and abilities. [D'Angelo 1998/02/03]
T.1.Ruling.2- Many players really want to know about the "speed" of a spell or ability. The truth is that "speed" isn't a very important concept in Magic. The type of a spell/ability really just determines when it can be played rather than how "fast" it is. Artifacts (and artifact creatures), creatures, sorceries, and enchantments are _not_ slower to resolve than instants. The only difference is when they can be announced. [D'Angelo 1998/02/03]
Note- Also see Delayed Abilities, Rule A.5.
Note- Also see Mana Abilities, Rule A.6.
Note- Also see Triggered Abilities, Rule A.4.