A quick Google turns up some definitions:
- a storytelling convention that writers often use, consciously or not. Big Bad is ubiquitous, but it's not a cliché. ... Every story uses tropes because, when used well, they work. A trope that is overused to the point of becoming tedious is a cliché.
- any plot, character, setting, device, or pattern that we recognize as such. ... What we don't like is when tropes are predictable to the point of boredom. That's when a trope becomes a cliche.
- simply a label for words that say one thing but mean another. In essence, it's a synonym for "literary device," because it's all-encompassing. A trope can be a metaphor, a simile, an example of personification, verbal irony, and more. In more contemporary usage, it can be a synonym for cliché too.
- a word or expression used in a figurative sense : figure of speech.
- a common or overused theme or device : cliché
- A trope can become a cliché if it's overused