The abohm is the derived unit of electrical resistance in the emu-cgs (centimeter-gram-second) system of units (emu stands for "electromagnetic units"). One abohm is equal to 10-9ohms in the SI system of units; one abohm is a nanoohm.
The emu-cgs (or "electromagnetic cgs") units are one of several systems of electromagnetic units within the centimetre gram second system of units; others include esu-cgs, Gaussian units, and Lorentz-Heaviside units. In these other systems, the abohm is not one of the units.
The name abohm was introduced by Kennelly in 1903 as a short name for the long name (absolute) electromagnetic cgs unit of resistance that was in use since the adoption of the cgs system in 1875. The abohm was coherent with the emu-cgs system, in contrast to the ohm, the practical unit of resistance that had been adopted too in 1875.