Flash

Flash is a keyword ability which allows the card it is printed on to be cast at any time you could cast an Instant.

Description
Flash first appeared in the Time Spiral expansion, its first appearance in a core set was in Tenth Edition. Although this ability existed before Time Spiral, this is the first time it was used a keyword. The earliest card with Flash is King Cheetah from Visions. Older cards with this ability have received errata to give them Flash.

Flash used to be primary in blue, secondary in green and black and tertiary in white and red. Starting with Kaldheim, white also became secondary to help solve its problems in Commander.