Standard is a rotating group of Magic: The Gathering sets. Most sets enter Standard when they're released and drop out about twenty-one months later. At any given time, Standard contains between five and eight sets.
Brawl is a format based on Standard—all rotations listed here apply to Brawl—but Brawl has a separate banlist.
Not all sets enter Standard upon release. For example, Masters sets and Commander sets do not enter Standard.
Despite being in Standard sets, these cards are explicitly not allowed in Standard decks.