Perpetual bond refers to a bond with no fixed repayment date or a long term, and the holder can get interest on schedule, but can't ask for repayment of the principal. The issuer may redeem in advance or have the right to postpone the maturity date.
The issuers of perpetual bonds are mainly state-owned enterprises, and many issuers count perpetual bonds into equity instruments for accounting, so the issuance of perpetual bonds has played a role in reducing leverage for state-owned enterprises with high debt ratio to some extent. Moreover, enterprises do not have to worry about the participation of perpetual bondholders in the company's operation and the dilution of equity.