This term has been discussed on this forum, e.g. under Examples of Kuhn loss?, and has been attributed to Kuhn himself. The term refers to the loss of explanations and predictions of the prior paradigm in the paradigm that replaced it. Cartesian mechanical explanations of gravity, and unification of various phenomena by the phlogiston theory are commonly given as examples.
The term was first suggested by the late Heinz Post from King's College in London in a 1971 article. Post claims that there is no Kuhn loss.
Here is the reference: Post, Heinz R. (1971), Correspondence, Invariance and Heuristics: In Praise of Conservative Induction, Studies in History and Philosophy of Science, 2, 213-255.
(It so happens that Post was my PhD advisor.)