Trope

A trope is a recognisable storytelling convention that lets a writer use the audience's familiarity as shorthand, rather than building the same understanding from scratch.

The distinction that settles most arguments comes from the TV Tropes wiki: tropes are not inherently disruptive to a story; a trope becomes a cliché when it turns intrusive — when it distracts the viewer rather than serving as shorthand.

That is a functional test rather than a taste one, and it is the reason "avoid tropes" is bad advice. The mentor, the heist crew, the reluctant chosen one, the locked-room mystery: these are the conventions that let a reader arrive already knowing how the machine works, so the writer can spend the pages on what is different. Genre readers do not want the conventions removed. They are, in large part, why the book was bought — which is also what comp titles communicate to an agent.

The useful move is the counterpoint: take the expectation the audience brings and put one thing against it. Hannibal Lecter, the cultured cannibal. Shrek, the sentimental ogre. The trope still does its job of orienting the reader, and the contradiction is what makes the character memorable.

A trope has gone wrong when the reader recognises the move rather than the moment — when they can see the author reaching for it.