A company that sells things often sells the same kind of thing at several prices — a cheap model, a middle model, an expensive model. That whole set is the 'range'. Top-of-the-range means the most expensive, best-equipped model in that set: 'a top-of-the-range washing machine', 'the top-of-the-range model costs twice as much'. So it is not simply praise like 'top-notch'. It tells you where something sits among its brothers and sisters from the same maker. A top-of-the-range car from a cheap brand may still be worse than a basic car from an expensive brand — the phrase compares inside one product line, not across the whole world. It is used mostly for machines and goods you buy: cars, phones, cameras, kitchen equipment, bicycles. It is British; Americans usually say 'top-of-the-line'. Both are ordinary, everyday words used in shops and adverts. Write it with hyphens before a noun ('a top-of-the-range camera'); after 'be', people often drop them ('this model is top of the range').