In the 1700's "Well Regulated" meant to do regularly, in ths aspect of the Militia: trained and equipped. The Militia and the NG not the same., Under the United States Code of  Law Sec. 311 defines the militia as the people in general. Members of the NG are paid, and that makes them a professional army, something the Founders abhorred , and the militia are unpaid, and serve in the common defense of state and country.