A more thorough explanation:

A common-law seal is a fastening that must be broken before access can be obtained. It is a device or substance that joins two things, usually making the seam impervious. It is also a piece of wax, a wafer, or some other substance affixed to the paper or other material on which a promise, release, or conveyance is written, together with a recital or expression of intention by which the promisor, releasor, or grantor manifests that a piece of wax, wafer, or other substance is a seal. The purpose of a seal is to secure or prove authenticity.

For example, a corporate seal is a seal adopted by a corporation for executing and authenticating its corporate and legal instruments. A notary seal is a seal used by a notary public to certify documents. A great seal is the official seal of the United States or a particular state. A private seal is a corporate or individual seal, as distinguished from a public seal.

These examples illustrate how different types of seals are used to authenticate or certify documents and instruments, and to prove their authenticity.