The term Hate refers to a hate card, which is a card that is particularly powerful against a certain card type or color. An example is Naturalize, which is an enchantment hate card because it destroys enchantments. Hate cards are generally in the sideboard, so you swap them into your deck when you face a deck with a certain card type (e.g. Artifacts) or a deck of a certain color (e.g, Black).
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