Electrical conductance, G, is the reciprocal of resistance (R):
Electrical conductance measures how easily electricity flows through electrical components for a given voltage difference. The SI unit of conductance is siemens (the older unit was the mho). Generally, people prefer to think in terms of resistances rather than electrical conductance, although neither is actually more fundamental. This is particularly true in the case of Ohm's law.
Electrical conductance is closely related to electrical conductivity. Electrical conductance is a property of a particular electrical component (like a particular wire), while conductivity is a property of the material itself (like silver).