Who the Agent Is
The term "agent" is usually used in at least two (or three) meanings, which are often mixed up by people who are not specialists. In the media the term can have two different meanings. It is either a secret co-operator of an intelligence service or a police force or it is a member of these organizations.
"Agent" is derived from the Latin word "agens" = active and it has many uses and meaning in common language and various scientific disciplines.
In the context of intelligence and secret police, the term had been used in Europe since the middle of the 19th century in only one meaning i.e. "secret co-operator", often with a negative connotation, pejoratively - meaning "informer, squealer, grass". A secret co-operator is defined as a person who is not an employee of the police or secret services. It can be anybody; he/she is in a secret contact with the (operative) officer of the service or the police organization and this officer assign him/her (the agent) tasks and controls his/her activities. There are many types of secret co-operators. The officer, by contrast, is a state employee in the service.
Intelligence service and police organizations define the secret co-operators in their internal regulation and terminology differently. It is possible that different services in one country use different "official" expressions for the same term.
Similar to continental Europe, Great Britain has also distinguished between the officers and the agents, i.e. secret co-operators, although in literature these terms have been sometimes mixed up (Joseph Conrad, Graham Greene).
The usage of the term "agent" changed in the 1930s, when in the USA the federal police bodies, especially FBI, were formed or were strengthened. The FBI officer (intelligence operative = detective = investigator) often has the rank of Special Agent. If special agents use and control their secret co-operators, they call them informers. The Drug Enforcement Administration (DEA) and other U.S. services use the term "agent" similarly.
After the media, popular literature and Hollywood cinematography started to use the activity of the FBI as their favourite theme, the term "agent" started to be used mainly to call the officer of the intelligence services or police organizations. The U.S. usage of the word gradually spread throughout the world and today the media use and mix up both terms. Unfortunately, there is nothing we can do about it. We can understand the correct meaning only from the context and it is often very difficult.
On the other hand, the CIA (not to mention the British services) officially uses the term "agent" only for a secret co-operator (a member of the CIA is called "officer" or "employee" or "career staff member").
In Communist Czechoslovakia, the STB (former communist secret service) regulation used the term "agent" for the most important type of secret co-operators. Hence the term had negative connotations after the fall of the communist regime.
After the November 1989 the legislation tried to find a new term for the secret co-operator and the legal language introduced the term "person acting for the benefit of secrete services". This is the right equivalent for an "agent" (however, this term is used in unofficial jargon by services all over the world, except for the FBI).
The amendment of the Czech criminal and police law introduced the term "agent" again in 1995, however, its meaning is completely different, as it means " a special police forces' member who is sent to work under cover for instance in organized crime" (in the FBI terms it would be an undercover policeman).
The term "agency" can then be used for a group of secret co-operators (agent network) or for an organization or an institution.
Source: Petr Zeman - lectures, trainings and public speeches