That being said, the 5th Circuit's Emerson case said that you don't have to be an active member of the militia in order to be protected by the 2nd Amendment. Thus, the actual definition of militia is, while historically interesting, not that important for legal purposes at present. It does, however, help to confuse/piss off lieberals to tell them that they are members of the militia.
U.S. Code Title 10 defines militia as: "All able-bodied males at least 17 years of age and under 45 years of age who are, or who have made a declaration of intention to become, citizens of the United States and of female citizens of the United States who are members of the National Guard. The classes of the militia are (1) the organized militia, which consists of the National Guard and the Naval Militia; and (2) the unorganized militia, which consists of the members of the militia who are not members of the National Guard or the Naval Militia." This means we -- the citizens -- are the militia.