1 : having or composed of four items or elements : quadruple sense 1 The F/A-18 flight-control system … is characterized by quad redundancy, which means that there are essentially four levels of sensing and actuation for each control surface. — McGraw-Hill Yearbook Of Science And Technology Quad skates are roller skates that have four wheels arranged in two rows, while inline skates have them in one line.— Jenee Osterheldt

2 : quadraphonic Domestic quad listening needs two additional loudspeakers over stereo, and two more amplifiers, plus the black box which allocates some of the sounds to the rear left/right, and others to the front left/right.— George Steedman

quad

noun (4)

Definition of quad (Entry 6 of 8)

: quadraphonic sound

quad

noun (5)

Definition of quad (Entry 7 of 8)

: a unit of energy equal to one quadrillion British thermal units

quad

noun (6)

plural quads

Definition of quad (Entry 8 of 8)

informal

: the greater extensor muscle of the front of the thigh that is divided into four parts : quadriceps —usually plural"Usually after a heptathlon I can tell if I'm not going to do well jumping. My quads get tired."— Jackie Joyner-KerseeDick Williams, Seattle manager, on shortstop Spike Owen's injured quads: "I never had any quads when I played." — Sports Illustrated