What is an Anti Fuse ?

An Anti fuse is a device which fuses when there is a high voltage across it.  Just as a fuse opens the circuit in the case of an abnormality, the antifuse closes the circuit in the event of an abnormality.

An antifuse is an electrical device that performs the opposite function to a fuse. Whereas a fuse starts with a low resistance and is designed to permanently break an electrically conductive path (typically when the current through the path exceeds a specified limit), an antifuse starts with a high resistance and is designed to permanently create an electrically conductive path (typically when the voltage across the antifuse exceeds a certain level). This technology has many applications.

The fuse and antifuse are components with completely opposite operating characteristics.
Fuse consists of a conductive filament of low resistance & it is used for protection against over-current.  When current higher than rated flows through fuse, due to (I^2)*R loss heat is produced and it leads to melting of fuse element. Thus disconnecting appliance from mains supply.

An antifuse starts with a high resistance and is designed to permanently create an electrically conductive path (typically when the voltage across the antifuse exceeds a certain level).