Typically, size of the rooms, quality of furnishings, quality of services provided- and the price.
There is no set number- It varies from one hotel to another. I know of two in Hawaii about a half mile apart- one has 600 rooms, the other has 12.
Luxury hotels are classified as five star hotels. Rates for accommodation are very high and generally used by people who can spend a lot of money: the rich, VIP class people, big investors,...
The Avalon Beach Hotel in Bournemouth is considered a luxury hotel and has won awards on Tripadvisor in the UK and Europe.
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