The term tier 2 capital refers to one of the components of a bank's required reserves. Tier 2 is designated as the second or supplementary layer of a bank's capital and is composed of items such as revaluation reserves, hybrid instruments, and subordinated term debt. It is considered less secure than Tier 1 capital—the other form of a bank's capital—because it's more difficult to liquidate. In the United States, the overall capital requirement is partially based on the weighted risk of a bank's assets.