Any quarterback who is capable of beating his opponent with both his running and passing ability.
Michael Vick is one of the best dual-threat quarterbacks to ever play in the National Football League. The perfect example of this came during a game on November 15, 2010. Vick amassed 431 combined yards of total offense (333 yards passing and 80 yards rushing, and 6 total touchdowns) in leading the Philadelphia Eagles to a 59-28 win over the Washington Redskins.
Other great dual-threat quarterbacks include Steve Young and Fran Tarkenton, both Pro Football Hall of Fame inductees.