Combatant is the legal status of an individual who has the right to engage in hostilities during an international armed conflict. The legal definition of "combatant" is found at article 43 of Additional Protocol One to the Geneva Conventions of 1949 [AP1]. It states that "Members of the armed forces of a Party to a conflict (other than medical personnel and chaplains covered by Article 33 of the Third Convention) are combatants, that is to say, they have the right to participate directly in hostilities." 
In addition to having the right to participate in hostilities, combatants have the right to status of Prisoners of War when captured during an international armed conflict.  " While all combatants are obliged to comply with the rules of international law applicable in armed conflict, violations of these rules shall not deprive a combatant of his right to be a combatant or, if he falls into the power of an adverse Party, of his right to be a prisoner of war."
Members of other militias and members of other volunteer corps, including those of organized resistance movements, belonging to a party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that they fulfill the following conditions:
that of being commanded by a person responsible for his subordinates;
that of having a fixed distinctive sign recognizable at a distance;
that of carrying arms openly;
that of conducting their operations in accordance with the laws and customs of war.
Members of regular armed forces who profess allegiance to a government or an authority not recognized by the Detaining Power.
Inhabitants of a non-occupied territory, who on the approach of the enemy spontaneously take up arms to resist the invading forces, without having had time to form themselves into regular armed units, provided they carry arms openly and respect the laws and customs of war.
For countries which have signed the "Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts" (Protocol I), combatants who do not wear a distinguishing mark still qualify as prisoners of war if they carry arms openly during military engagements, and while visible to the enemy when they are deploying to conduct an attack against them.