ما معنى Contingent convertible bond, additional tier 1؟

A contingent convertible bond (CoCo) is a bank bond that is converted into shares or written down when a trigger is hit, such as the bank’s common equity ratio falling below a level set in the bond. Additional tier 1 (AT1) capital consists of perpetual instruments, usually CoCos, whose coupons the bank may cancel and which absorb losses while the bank is a going concern; they rank above common equity and below all other debt in a liquidation.