What's the opposite of a Pareto improvement called? Wikipedia defines a Pareto Improvement, "given a certain initial allocation of goods among a set of individuals" as:


  a change to a different allocation that makes at least one individual or preference criterion better off without making any other individual or preference criterion worse off


Given this definition, then, the opposite of a Pareto Improvement should be:


  a change to a different allocation that makes at least one individual or preference criterion worse off without making any other individual or preference criterion better off.


What's the correct way to refer to this? Does it have a name?
I usually use the phrase "Pareto worsening". It is not really widespread, in fact I am not sure I have ever heard anyone else use it. However now I googled it and people seem to use it in connection with Hart's 1975 paper wherein he shows that the opening of some new markets can make every agent worse off. Hart himself did not call this Pareto worsening, but other scholars do. An example is on page 230 of volume II of General Equilibrium, Growth, and Trade. Here is the same phrase used in Information and Securities: A Note on Pareto Dominance and the Second Best.