Trope

A trope, in the word's original sense, is "any instance of figurative (non-literal) language, such as a metaphor, hyperbole, or personification." In modern usage the meaning "has also broadened to mean any commonly recurring idea, phrase, image, artistic technique, artistic element, or cliché," and that is the sense writers use: a situation, character, plot structure or object that "commonly appears or recurs across works within a particular genre or narrative medium," from the transportation accident that opens an isekai to the cliffhanger that ends a chapter.

Conventions "are the very features that are expected of, and may even define, a given genre." Tropes are therefore the genre contract: readers arrive knowing the moves, so the craft decision is fulfillment for comfort, combination for novelty, or subversion for surprise. A web serial's tags, LitRPG or cultivation or harem, are bundles of tropes promised before chapter one.