Related Rule
Russian Federation
Practice Relating to Rule 5. Definition of Civilians
The Russian Federation’s Regulations on the Application of IHL (2001) states:
civilian is any person present in the area of combat operations, who is not a member of armed forces and refrains from any act of hostility. In case of doubt whether a person is a civilian, that person shall be considered a civilian;
civilian population is a population which consists of civilians. 
Russian Federation, Regulations on the Application of International Humanitarian Law by the Armed Forces of the Russian Federation, Ministry of Defence of the Russian Federation, Moscow, 8 August 2001, § 1.
The Report on the Practice of the Russian Federation notes that although there is no standard definition of civilians, a definition can be inferred a contrario from the definition of combatant, i.e. civilians are those who do not fall within the definition of combatant. 
Report on the Practice of the Russian Federation, 1997, Chapter 1.1.