Combatant in the context of "Trench warfare"

A mercenary is a private individual who joins an armed conflict for personal profit, is otherwise an outsider to the conflict, and is not a member of any other official military. Mercenaries fight for money or other forms of payment rather than for political interests.

Beginning in the 20th century, mercenaries have increasingly come to be seen as less entitled to protection by rules of war than non-mercenaries. The Geneva Conventions declare that mercenaries are not recognized as legitimate combatants and do not have to be granted the same legal protections as captured service personnel of the armed forces. In practice, whether or not a person is a mercenary may be a matter of degree, as financial and political interests may overlap.

Total war is a type of warfare that mobilizes the totality of national resources to sustain war production, blurring the line between military and civilian activities and legitimates attacks on civilian targets as part of a war without restriction as to the combatants, territory or objectives involved.

The term has been defined as "A war that is unrestricted in terms of the weapons used, the territory or combatants involved, or the objectives pursued, especially one in which the laws of war are disregarded."

Combat is a purposeful violent conflict between multiple combatants with the intent to harm the opposition. Combat may be armed (using weapons) or unarmed (not using weapons). Combat is resorted to either as a method of self-defense or to impose one's will upon others. An instance of combat can be a standalone confrontation or part of a wider conflict, and its scale can range from a fight between individuals to a war between organized groups. Combat may also be benign and recreational, as in the cases of combat sports and mock combat.

Combat may comply with, or be in violation of, local or international laws regarding conflict. Examples of rules include the Geneva Conventions (covering the treatment of people in war), medieval chivalry, the Marquess of Queensberry Rules (covering boxing), and the individual rulesets of various combat sports.

A casualty (/ˈkæʒuəlti/ KAZH-oo-əl-tee, UK also /ˈkæʒjuəlti/ KAZH-yoo-əl-tee), as a term in military usage, is a person in military service, combatant or non-combatant, who becomes unavailable for duty due to any of several circumstances, including death, injury, illness, missing, capture or desertion.

In civilian usage, a casualty is a person who is killed, wounded or incapacitated by some event; the term is usually used to describe multiple deaths and injuries due to violent incidents or disasters. It is sometimes misunderstood to mean "fatalities", but non-fatal injuries are also casualties.

Distinction (principle of distinction) is a principle under international humanitarian law governing the legal use of force in an armed conflict, whereby belligerents must distinguish between combatants and protected civilians. Combatant in this instance means persons entitled to directly participate in hostilities and thus are not afforded immunity from being directly targeted in situations of armed conflict. Protected civilian in this instance means civilians who are enemy nationals or neutral citizens outside of the territory of a belligerent power.

Article 51.3 of the 1977 Additional Protocol I to the Geneva Conventions explains that “civilians shall enjoy the protection afforded by this section, unless and for such time as they take a direct part in hostilities.” Distinction, proportionality, and precaution are important factors in assessing military necessity in that the harm caused to protected civilians or civilian property must be proportional and not "excessive in relation to the concrete and direct military advantage anticipated" by an attack on a military objective.

A sapper, also called a combat engineer, is a combatant or soldier who performs a variety of military engineering duties, such as breaching fortifications, demolitions, bridge-building, laying or clearing minefields, preparing field defenses, and road and airfield construction and repair.

Sappers are also trained and equipped to serve secondarily as provisional infantry.

Body armour, personal armour (also spelled armor), armoured suit (armored) or coat of armour, among others, is armour for a person's body: protective clothing or close-fitting hands-free shields designed to absorb or deflect physical attacks. Historically used to protect military personnel, today it is also used by various types of police (riot police in particular), private security guards, or bodyguards, and occasionally ordinary citizens. Today there are two main types: regular non-plated body armor for moderate to substantial protection, and hard-plate reinforced body armor for maximum protection, such as used by combatants.

Tactical bombing is aerial bombing aimed at targets of immediate military value, such as combatants, military installations, or military equipment. This is in contrast to strategic bombing, or attacking enemy cities and factories to cripple future military production and enemy civilians' will to support the war effort, to debilitate the enemy's long-term capacity to wage war. The term "tactical bomber" only refers to a bomber aircraft designed specifically for the primary role of tactical bombing, even though many other types of aircraft ranging from strategic bombers to fighters, interceptors, and helicopters have been used in tactical bombing operations.

Tactical bombing is employed for two primary assignments. Aircraft providing close air support attack targets in nearby proximity to friendly ground forces, acting in direct support of the ground operations (as a "flying artillery"). Air interdiction, by contrast, attacks tactical targets that are distant from or otherwise not in contact with friendly units.