Widget

In the APG, an interactive interface building block a person operates to do something or move through content — a button, a combobox, a slider, a tab list

The line is operability, not appearance: a widget is something you act on, which is why it needs a role, a name, a state and keyboard behavior. A heading and a landmark are structure — they organize and label, and a reader navigates by them rather than operating them. That distinction decides whether a thing needs arrow keys and aria-expanded, or only a sensible tag.

In the Agentic DS draft's kind enum, a component with state of its own and no open composition slot — a button, an image-compare slider, a video player, a rating control

Close enough to the APG sense that the name holds: it is something a person operates. It has no slots of its own and adds one to the nesting depth. It may nest inside another component only where that component's statefulAllows lists it. A video player is a region holding several APG widgets, but with no open slot it counts as one widget here.

In everyday product talk, any self-contained bit of interface — a weather widget, a dashboard widget

Looser and older, and worth separating because the APG sense carries obligations the loose one does not. A 'dashboard widget' that is really a card with some numbers is structure, not a widget in the APG's sense, and giving it a role because the word matched would make it worse.