A heuristic evaluation is a careful review of an app or website using a list of common usability guidelines. It is like checking a room against a safety checklist instead of waiting for someone to trip.
A reviewer may ask: can people tell what is happening, undo a mistake, and understand the words on the screen? They record the problem and where it appears.
This review can find obvious trouble early, but it does not replace watching real people use the product. A guideline suggests what to inspect; user feedback helps confirm what actually causes difficulty.