Instant

Instants, like sorceries, represent one-shot or short-term magical spells. They are never put onto the battlefield; instead, they take effect when their mana cost is paid and the spell resolves, and then are immediately put into the player's graveyard.

Instants are the only card type in Magic, something unique to it compared to other card games, to have no timing restrictions. They can be played at any time one has priority, including during other player's turns and while another spell or ability is waiting to resolve.

Due to the immense design space of flash, and how Instant is the only card type without timing restrictions, the idea has been floated that Instant could have been removed as a type and all current Instants turned to Sorceries with a subtype that grants "instant speed", and other card types would also use this subtype to gain "instant speed", like how Flash is used now. This would also simplify the rules regarding casting spells, subtyping, and collective references. Due to the strong inertia, this is seen as an unlikely to impossible change.

Subtypes
The subtype for instants is called spell type and shared with sorceries.

Friendly to instants
Blue and red are the two colors that most appreciate instants and reward the player for playing them.

Instant speed
The informal term "instant speed" means "whenever you would be able to cast instant spells". This is most often used by the keyword Flash, granting "instancy" to any card type. Some abilities have "sorcery speed" baked into their rules, and some cards allow them to be activated "any time you could cast an instant". However, the timing restriction has been used to turn mana abilities into non-mana abilities, most famously Lion's Eye Diamond - this is to prevent it from casting spells, as part of the process of casting a spell is putting the spell from the hand onto the stack before paying costs. Starting with Strixhaven: School of Mages, the card text "only any time you could cast an instant" was shortened to "activate as an instant."

The opposite of instant speed is sorcery speed.

Obsolete card types
The cards with the types mana source or interrupt became instants.