Complex electrical term/ratio/quantity with symbol, Y, analogous to the inverse of impedance, Z, of a circuit, i.e., the ration of the current to the voltage in a circuit taking into account phase. Y = I / V A standard physics term for the velocity of light in vacuum/air (absolute). c = 3 x 10 m/sec. Also inversely related to absolute To (Air Time Delay) = 3.3333 ns/m.