A regular army is the official army of a state or country (the official armed forces), contrasting with irregular forces, such as volunteer irregular militias, private armies, mercenaries, etc. A regular army usually has the following:
Irregular military is any military component distinct from a country's regular armed forces, representing non-standard militant elements outside of conventional governmental backing. Irregular elements can consist of militias, private armies, mercenaries, or other non-state actors, though no single definition exists beyond exclusion from national service. 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 infantry and irregular cavalry units.
Irregular warfare is warfare employing the tactics commonly used by irregular military organizations. This often overlaps with asymmetrical warfare, avoiding large-scale combat and focusing on small, stealthy, hit-and-run engagements.