Bond is a debt instrument, the purpose of the issuance of bonds is to raise funds by borrowing from the public. Generally, there are terms for each bonds stating the maturity date which principals will be repaid and the coupon interest payment date.
The bonds issue by state or government in its currency. For example, The US department of the Treasury issues bond s to raise funds for the US government.
The bonds issue by public corporations, which level is lower than government bonds, but the credit ratings of these two bonds are normally the same. E.g.: The Hong Kong Airport Authority (HKAA), Hong Kong Mortgage Corporation Limited (HKMTGC)
Mostly issue by private corporations. E.g.: Hutchison Whampoa Limited