Wikipedia
Mesoeconomics or Mezzoeconomics is a neologism used to describe the study of economic arrangements which are not based either on the microeconomics of buying and selling and supply and demand, nor on the macroeconomic reasoning of aggregate totals of demand, but on the importance of the structures under which these forces play out, and how to measure these effects. It dates from the 1980s as several economists began questioning whether there would ever be a bridge between the two main economic paradigms in mainstream economics, without wanting to discard both paradigms in favor of some other basic methodology and paradigm.
Mesoeconomics is not a generally recognized term, and it has only a small number of adherents compared to microeconomics or macroeconomic. Several books on this topic including Mann in 2011 and Ng in 1987 help define the scope of mesoeconomics. Scholarly articles on the topic are starting to increase in number with 474 articles and books on the topic in a database search in July, 2014. The term Mesoeconomics is still emerging and should be used with restraint due to unfamiliarity with most audiences.
The term comes from "meso-" (which means "middle") and "economics", and is constructed in analogy with micro and macro economics.