It is a surprising fact that something can be sold under two rubrics; what it is and expressly what it is not. Mock Turtle Soup is in that category. What is it?
It is expressly fake. However, what is fake is the soup, not the turtle. The turtle is absent. It had to be absent, because it was rare and expensive. However, it had a consistency and mock turtle soup is an effort to produce the same consistency as the real thing.
Check the recipe for Mock Turtle Soup.
What is more common is a passing off of something, or someone, for what they are not.
Charladies, for instance, are not ladies nor are lady friends ladies. These are terms of mock gentility and express class-based anxieties.
A current Irish example is using the appellation “Mr. Justice……….”, where the individual is not a judge at all.