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A covert human intelligence source who has undergone a period of assessment and whose reporting has been validated. To be distinguished from an officer (a member of staff) of SIS.

Acronym occasionally used for SIS - British Secret Intelligence Service to distinguish us from others with similar acronyms - CSIS (Canadian Security Intelligence Service), ASIS (Australian Secret Intelligence Service) and NZSIS (New Zealand Security Intelligence Service).

Chief of SIS. Used in honour of the first Chief of SIS, Sir Mansfield Cumming, who habitually signed himself 'C'.

SIS intelligence reports as issued to customers.

Central government department with responsibilities for co-ordinating the UK national intelligence machinery.

Defence Intelligence Staff.  Intelligence analytical organisation of the Ministry of Defence traditionally serving the UK armed forces but also serving wider government customers.

. The UK ministry of foreign affairs. 

. The UK sigint (signals intelligence) agency.  One of SIS's two sister intelligence and security agencies along with the Security Service.

Government Code and Cipher School. Forerunner of GCHQ. Part of  SIS from 1923 to 1947.

Human intelligence or intelligence derived from human sources. 

The UK ministry of the interior.

. A key piece of UK legislation to which SIS is subject.

. This act placed SIS on a statutory footing and defines what the Service may do.

Joint Intelligence Committee. Part of the Cabinet Office and the central body of the national intelligence machinery. It advises on the priorities for intelligence collection and assesses Agency performance against those priorities.

Joint Terrorism Analysis Centre. Sits within the Security Service to analyse all source intelligence on terrorist threats to the UK and UK interests.  Staffed by members of all three intelligence and security agencies and the , , , the Police and other government departments.

Foreign intelligence services with which SIS cooperates. It is SIS policy not to comment on its relationships with liaison services.

Commonly used but dating back to before WWII.

Commonly used but unofficial title for the

A member of SIS staff. Often confused in popular vocabulary with agent.

An intelligence gathering operation.

Intelligence requirements set by the .

. Regulatory Act which established a Commissioner for Interception, a Commissioner for the Intelligence Services and the .

The Secret Intelligence Service, also known as MI6.

The Special Operations Executive. WWII clandestine operations agency absorbed into SIS towards the end of the war. Security-edited records from the period before absorption have been released by SIS to the UK National Archive.

Any source of information or intelligence. An agent may be a source but a source is not automatically an agent.

Signals intelligence. The primary task of

Information acquired against the wishes and generally without the knowledge of the originators or possessors. Sources are kept secret from readers as are the techniques used to acquire the information. Intelligence provides privileged insights not available openly.

. The budget through which all three intelligence and security agencies are funded.