Heavy ICBM is a term that was created in the 1970s to describe a class of SovietICBMs (intercontinental ballistic missiles). They were characterized by a heavy throw-weight of 5 to 9 metric tons, several times that of an LGM-30 Minuteman, and a length of over 35 meters, and were thus capable of delivering a large number of warheads in a single MIRV missile.
The SS-9 was a silo-launched missile capable of delivering warheads of 5 - 18 megatons, with a range of up to 15,500 km, greater than the diameter of the Earth. These were then replaced by the similar SS-18, with payloads of 18 - 25 megatons. The silos used for launching were the same for both, once modified.