Credential

A credential is an attestation of qualification, competence, or authority issued to an individual by a third party with a relevant or de facto authority or assumed competence to do so.

Examples of credentials include academic diplomas, academic degrees, certifications, security clearances, identification documents, badges, passwords, user names, keys, powers of attorney, and so on. Sometimes publications, such as scientific papers or books, may be viewed as similar to credentials by some people, especially if the publication was peer reviewed or made in a well-known journal or reputable publisher.

A person holding a credential is usually given documentation or secret knowledge (e.g., a password or key) as proof of the credential. Sometimes this proof (or a copy of it) is held by a third, trusted party. While in some cases a credential may be as simple as a paper membership card, in other cases, such as diplomacy, it may involve presentation of letters directly from the issuer of the credential detailing its faith in the person representing them in a negotiation or meeting.

Counterfeiting of credentials is a constant and serious problem, irrespective of the type of credential. A great deal of effort goes into finding methods to reduce or prevent counterfeiting. In general, the greater the perceived value of the credential, the greater the problem with counterfeiting and the greater the lengths to which the issuer of the credential must go to prevent fraud.

In diplomacy, credentials, also known as a letter of credence, are documents that ambassadors, diplomatic ministers, plenipotentiary, and chargés d'affaires provide to the government to which they are accredited, for the purpose, chiefly, of communicating to the latter the envoy's diplomatic rank. It also contains a request that full credence be accorded to his official statements. Until his credentials have been presented and found in proper order, an envoy receives no official recognition.

...
Wikipedia