An excerpt from an OUPblog article published on 1st March 2017, written by Nigar Hashimzade and Gareth Myles, co-authors of A Dictionary of Economics.
'There are some economic terms that are fixed and immutable. Marginal cost will always be the addition to cost from an incremental increase in output, and average cost will never be anything other than total cost divided by output. Other terms have greater fluidity and evolve over time with developments in theory and practice. For this reason, compilation of the Dictionary is never finished and definitions are never final.
The original notion of equilibrium in economics referred to the equality of supply and demand. It then expanded to include the Nash equilibrium, and now includes numerous concepts of equilibrium in dynamic situations, situations under uncertainty, in the strategic games with complete and incomplete information, and so on.'
Discover more: Read the rest of the article on the OUPblog.