Prop

A configuration value of a Component Schema, drawn from a small set the design system defines or a boolean, and keyed by scope: props.component for one value per instance, props.item for one value per repeated item

Two tests decide prop against shape. Boundedness: a closed set of valid values is a prop, an open-ended one is shape. Who and when: a prop is set once by whoever configures the component. A third test decides prop against token contract: would an author set this differently for one specific instance? If so it's a prop (allowMultipleOpen, treatment); if it's a design decision that should look the same everywhere, it's a touchpoint. Scope keys other than component must match exactly one repeating array in the shape, by its singular name.

In front-end frameworks, an input a parent passes to a child component

The framework sense is mechanical and covers content too. The schema sense is narrower: content belongs to shape, and only configuration is a prop.