The term civil service has two distinct meanings:

• A branch of governmental service in which individuals are employed on the basis of professional merit as proven by competitive examinations.
• The body of employees in any government agency other than the military.

A civil servant or public servant is a civilian public sector employee working for a government department or agency. The term explicitly excludes the armed services, although civilian officials will work at "Defence Ministry" headquarters. The term always includes the (sovereign) state's employees; whether regional, or sub-state, or even municipal employees are called "civil servants" varies from country to country. In the United Kingdom, for instance, only Crown employees are referred to as civil servants, county or city employees are not.
Many consider the study of civil service to be a part of the field of public administration. Workers in "non-departmental public bodies" (sometimes called "QUANGOs") may also be classed as civil servants for the purpose of statistics and possibly for their terms and conditions. Collectively a state's civil servants form its Civil Service or Public Service.
Administrative institutions usually grow out of the personal servants of high officials, as in the Roman Empire. This developed a complex administrative structure, which is outlined in the Notitia Dignitatum and the work of John Lydus, but as far as we know appointments to it were made entirely by inheritance or patronage and not on merit, and it was also possible for officers to employ other people to carry out their official tasks but continue to draw their salary themselves. There are obvious parallels here with the early bureaucratic structures in modern states, such as the Office of Works or the Navy in 18th century England, where again appointments depended on patronage and were often bought and sold.
An international civil servant or international staff member is a civilian employee that is nominated by an international organisation. These international civil servants do not resort under any national legislation (from which they have immunity of jurisdiction) but are governed by an internal staff regulation. All disputes related to international civil service are brought before special tribunals created by these international organisations such as, for instance, the Administrative Tribunal of the ILO.
Specific referral can be made to the International Civil Service Commission (ICSC) of the UN, an independent expert body established by the United Nations General Assembly. Its mandate is to regulate and coordinate the conditions of service of staff in the United Nations common system, while promoting and maintaining high standards in the international civil service.