Here is another definition of Grade Inflation. This is from one of the external links in the article by Patrick Julius (March 2018):
"...when a grade is viewed as being less rigorous than it ought to be" (Mullen, 1995, p29).
I vacillated about posting this definition because it may be sufficiently nebulous as to be meaningless. Although it may have been meaningful to its intended audience, at that point in time (prior to Common Core).