…. an “individual who has claimed the right to refuse to perform military service” on the grounds of freedom of thought, conscience, and/or religion.

In some countries, conscientious objectors are assigned to an alternative civilian service as a substitute for conscription or military service. Some conscientious objectors consider themselves pacifist, non-interventionist, non-resistant, or antimilitarist.
The international definition of conscientious objection officially broadened on March 8, 1995 when the United Nations Commission on Human Rights resolution 1995/83 stated that “persons performing military service should not be excluded from the right to have conscientious objections to military service.” That definition was re-affirmed in 1998, when the United Nations Office of the High Commissioner for Human Rights document called “Conscientious objection to military service, United Nations Commission on Human Rights resolution 1998/77” officially recognized that “persons [already] performing military service may develop conscientious objections.”

Source: Wikipedia