A gold certificate in general is a certificate of ownership that gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 owners hold instead of storing the actual gold. It has both a historic meaning as a US paper currency (1882–1933) and a current meaning as a way to invest in gold.

Banks may issue gold certificates for gold which is allocated (non-fungible) or unallocated (fungible or pooled). Unallocated gold certificates are a form of fractional reserve banking and do not guarantee an equal exchange for metal in the event of a run

Bank run

A bank run occurs when a large number of bank customers withdraw their deposits because they believe the bank is, or might become, insolvent...

 on the issuing bank's gold on deposit.