Hubble constant - (n.)

The numerical factor, usually denoted H, that describes the rate of expansion of the universe. It is the proportionality constant in the Hubble law v ~Hd, which relates the speed of recession of a galaxy (v) to its distance (d) . The present value of H has recently become fairly well known; estimates range between 47 and 63 km/sec Y Mpc, giving an age of the universe around 14 billion years.