Paramilitary (from para ("beside") + military) refers to organizations formed on a military pattern, but not part of the official military.
The term may indicate an official or a semi-official status or a desire for such a status. Under the law of war, a state may incorporate a paramilitary organization or armed agency (such as a national police or a private volunteer militia) into its combatant armed forces. The other parties to a conflict have to be notified thereof.
In some countries, the term may refer to official semi-militarized law enforcement, guard, or volunteer organizations.
However, sometimes the term is used similarly to "irregular military" and may thus be used to label various completely non-official and even illegal organizations formed on a military pattern. For example, Wikipedia categorizes various illegal organizations in Ireland and Northern Ireland as "paramilitary organizations".