A seal generally is an impression made by a device, frequently an engraved metallic or stone plate, either on wax or a wafer affixed to an instrument or directly on the instrument itself. Seals are used by government agencies, corporations and notaries public to show that the document is validly executed, acknowledged or witnessed, since the seal is unique to the sealer.
For example, corporate seals state the name, date and state of incorporation. The corporate by-laws will specify the officer who is custodian of the corporate seal, where the seal should be kept, who can use the seal, and when the seal should be used. The seal is used to authenticate the document it is affixed on.