Format refers to the ways you can play standard matches. Playing in Rotation format allows you to play using the five most recent card sets and basic cards in a match. Unlimited format allows you to use all available cards in a match.
In Rotation format, you can use the five most recent card sets and basic cards in a match. This format is recommended for players new to Shadowverse.
In Unlimited format, players can use all available cards. Note that there may be some restrictions placed on cards.