Annulment is a legal procedure for declaring a marriage null and void. Annulment differs from divorce where the court ends an otherwise legal marriage on a specific date.
A strict terminology, annulment refers only to making a voidable marriage null; if the marriage is void ab initio, then it is automatically null, although a legal declaration of nullity is required to establish this.
The process of obtaining such a declaration is similar to the annulment process.