A term that is meant to try and describe saved electricity that by means of energy efficiency was not created, used or wasted. It is not yet a real physical amount or a measureable quantity, simply an attempt to popularize the thinking that saving electricity and making efficiency-efforts more fun and useful.
The potential in energy efficiency efforts in U.S. of reducing peak demand on electriciy is possibly as large as 60 Nuclear_Power_Plants of the infamous Chernobyl-sized plant.[1] (1989)
Compare this idea with the popular Benjamin Franklin quote: A penny saved is a penny earned[2]
Links
CCNR.org[3]
RMI.org[4]
Wikipedia/Negawatt_power[5]