blood alcohol content. The concentration of alcohol in one’s bloodstream, expressed as a percentage. • Blood alcohol content is used to determine whether a person is legally intoxicated, esp. under a driving-while-intoxicated law. In many states, a blood alcohol content of .08% is enough to charge a person with an offense. — Abbr. BAC. — Also termed blood alcohol count; blood alcohol concentration. See DRIVING UNDER THE INFLUENCE; DRIVING WHILE INTOXICATED . [Cases: Automobiles 332, 411. C.J.S. Motor Vehicles §§ 1382–1394, 1397–1411.]