What's the difference between three-star, four-star and five-star hotels? Is there a standard?

The difference between three-star, four-star and five-star hotels lies in the scale of five-star. Generally speaking, they have the largest facilities, perfect equipment, good service, fitness and spa, swimming, fitness and tennis. Rooms are decorated with high-grade decoration, excellent materials and perfect service. Four-star contrast with six-star is almost mainly reflected in the lack of five-star facilities, not to mention small scale, poor facilities and poor service.