A militia is generally an army or other fighting organization of non-professional and/or part-time soldiers, consisting of citizens of a country or subjects of a state who may perform military service during emergencies. Militias can be either military or paramilitary, depending on the instance. Some of the contexts in which the term "militia" can apply include forces engaged in a defense activity or service to protect a community, its territory, property, and laws, the entire able-bodied population of a community, town, county, or state available to be called to arms, a subset of these who may be legally penalized for failing to respond to a call-up, and a select militia composed of a small, non-representative portion of the population. Maritime militias composed of fishermen and other participants of the marine industry which are organized and sanctioned by a state to enforce its maritime boundaries are also included in the definition.

In the United States, the militia is defined in Chapter 12 of Title 10 of the United States Code as consisting of all able-bodied males at least 17 years of age and, except as provided in (b), the classes of the militia are the organized militia, which consists of the National Guard and the Naval Militia, and the unorganized militia, which consists of the members of the militia who are not members of the National Guard or the Naval Militia.

The term "militia" has taken on new meaning as makeshift vigilante groups have popped up with increasing frequency in the months leading up to a contentious election. The term has fundamentally lost its meaning as more groups use it to camouflage threats of violence.