Units of resistance are a measure of the opposition to the flow of electric current. Abohms (6 letters) is an abbreviation for abamperes per ohm, which is a unit of electrical resistance equal to 10 amperes per ohm. Ohms (4 letters) is the SI unit of electrical resistance, named after German physicist Georg Ohm. Rels (4 letters) is an abbreviation for roentgen equivalent in man, which is a unit of radiation exposure equal to the amount of gamma radiation that produces one electrostatic unit of charge in one cubic centimeter of dry air at standard temperature and pressure.