a fluid that exhibits frictionless flow, very high heat conductivity, and other unusual physical properties, helium below 2.186 K being the only known example.
su·per·flu·id (sōō'pər-flōō'ĭd) n. A fluid, such as a liquid form of helium, exhibiting a frictionless flow at temperatures close to absolute zero. su'per·flu·id'i·ty (-flōō-ĭd'ĭ-tē) n.