Combat
Hand-to-hand combat: Hand-to-hand combat (melee) is combat at very close range, attacking the opponent with the body (striking, kicking, strangling, etc.) and/or with a melee weapon (knives, swords, batons, etc.), as opposed to a ranged weapon.
Hand-to-hand combat can be further divided into three sections depending on the distance and positioning of the combatants:

Clinch fighting
Ground fighting
Stand-up fighting

Military combat: Military combat always involves between two or more opposing military forces in warfare. Military combat situations can involve multiple groups, such as guerilla groups, insurgents, domestic and/or foreign governments. A military combat situation is known either as a battle or a war, depending on the size of the fighting and which geographical areas in which it occurs. Combat effectiveness has always demanded that the personnel maintain strategic preparedness by being sufficiently trained, armed, equipped, and funded to carry out combat operations in the unit to which they are assigned. Warfare falls under the law of war, which govern its purposes and conduct, and protect the rights of combatants and non-combatants.

References: 

Sources: Martin van Creveld: The Changing Face of War: Lessons of Combat, from the Marne to Turkey. Maine, New England 2007.

Further reading: Wong, Leonard. 2006. "Combat Motivation in Today's Soldiers: U.S. Army War College Strategic Studies Institute."Armed Forces & Society, vol. 32: pp. 659–663.
Gifford, Brian. 2005. "Combat Casualties and Race: What Can We Learn from the 2003-2004 Iraq Conflict?" Armed Forces & Society, vol. 31: pp. 201–225.
Herspring, Dale. 2006. "Undermining Combat Readiness in the Russian Military, 1992-2005." Armed Forces & Society, Jul 2006; vol. 32: pp. 513–531.
Ben-Shalom, Uzi; Lehrer, Zeev; and Ben-Ari, Eyal. 2005. "Cohesion during Military Operations: A Field Study on Combat Units in the Al-Aqsa Intifada." Armed Forces & Society, vol. 32: pp. 63–79.
Woodruff, Todd; Kelty, Ryan; Segal, Archie Cooper, David R. 2006. "Propensity to Serve and Motivation to Enlist among American Combat Soldiers." Armed Forces & Society, Apr 2006; vol. 32: pp. 353–366.
Dienstfrey, Stephen. 1988. "Women Veterans' Exposure to Combat." Armed forces & Society, vol. 14: pp. 549–558.