Irregulars

Irregular military is any non-standard military, that is, distinct from that of the regular army. Being defined by exclusion, there is significant variance in what comes under the term. It can refer to the type of military organization, or to the type of tactics used.

An irregular military organization is one which is not part of the regular army organization. Without standard military unit organization, various more general names are often used; such organizations may be called a "troop", "group", "unit", "column", "band", or "force".

Irregulars are soldiers or warriors that are members of these organizations, or are members of special military units that employ irregular military tactics. This also applies to irregular troops, irregular infantry and irregular cavalry.

Irregular warfare is warfare employing the tactics commonly used by irregular military organizations. This involves avoiding large-scale combat, and focusing on small, stealthy, hit and run engagements.

The words "regular" and "irregular" have been used to describe combat forces for hundreds of years, usually with little ambiguity. Due to a government's chain of command requirements, the regular army is very well defined, and anybody fighting outside of that (excluding official paramilitary forces) are irregulars. In cases where the legitimacy of the army or its opponents is questioned, some legal definitions have been created.

In international humanitarian law, "irregular forces" refers to a category of combatants consisting of individuals forming part of the armed forces of a party to an armed conflict, international or non-international, but not belonging to that party's regular forces and operating in or outside of their own territory even if the territory is under occupation.

The Third Geneva Convention of 1949, uses "regular armed forces" as a critical distinction. The International Committee of the Red Cross (ICRC) is a non-governmental organization primarily responsible for, and most closely associated with, the drafting and successful completion of the Third Geneva Convention Relative to the Treatment of Prisoners of War ("GPW"). The ICRC provided commentary saying that "regular armed forces" satisfy four Hague Conventions (1899 and 1907) (Hague IV) conditions. In other words, "regular forces" must satisfy the following criteria:

...
Wikipedia