What it means
A marriage certificate is the official record of a marriage, issued by the Registry of Births, Deaths and Marriages in the relevant state or territory. The decorative certificate given on the wedding day is not the same as the official (registered) certificate. When applying for a divorce in Australia, you generally need to provide your official marriage certificate. If the marriage took place overseas, you can usually use the foreign certificate, with a translation and an accompanying affidavit if it is not in English. A standard certificate is ordered from the relevant registry, often for a fee.
How it's used
She ordered an official marriage certificate from the registry because she needed it to file her divorce application.