Single certificate, legally called "certificate of no marriage registration record", which is what we usually call unmarried certificate, is a written material used to prove that there is no marriage registration in the civil affairs department, so it is issued by the civil affairs department where the household registration is located.
In the past, not only unmarried, divorced and widowed, but also a single certificate was required to buy a house with a loan. You can't borrow money to buy a house without a single certificate. You don't have time to go to the civil affairs department to open it, so you can only entrust someone else to open it.
Just at the end of April this year, the Ministry of Civil Affairs and State Taxation Administration of The People's Republic of China issued the Notice on Strengthening the Cooperation between the Civil Affairs Department and the Tax Department to Enjoy Marriage Registration Information, indicating that the single certificate will no longer be issued. In other words, in the future, loans to buy a house no longer need a single certificate. Unmarried people borrow money to buy a house. If the bank insists on providing a marriage certificate, it can write a written statement about the marital status.