What it is
Gross profit is what's left after you subtract COGS from revenue. It's the money the company has to cover everything else — salaries, marketing, rent, R&D, taxes — and hopefully still have some left over.
Why people watch it
Gross profit is the rawest possible read on whether the core product is economic. A business with negative gross profit is selling each unit at a loss before any overhead. That's usually unsustainable.
A growing gross profit (faster than revenue) often signals pricing power or scale benefits in production.