describeCostCategoryDefinition

Returns the name, Amazon Resource Name (ARN), rules, definition, and effective dates of a cost category that's defined in the account.

You have the option to use EffectiveOn to return a cost category that's active on a specific date. If there's no EffectiveOn specified, you see a Cost Category that's effective on the current date. If cost category is still effective, EffectiveEnd is omitted in the response.