A bridge is an appliance permanently fixed in the mouth to replace missing teeth. It uses remaining teeth to support the new artificial tooth or teeth.

A conventional fixed bridge consists of crowns that are fixed to the teeth on either side of the missing teeth and false teeth rigidly attached to these crowns. 
An enamel bonded bridge uses a metal or porcelain framework., to which the artificial teeth are attached, then resin bonded to supporting teeth. (Source: Australian Dental Association)

To restore missing tooth/teeth, the teeth adjacent to the missing tooth are prepared to recieve crowns attached to an artificial tooth and permanently cemented - very convenient compared to a removable denture.