A startup is a business with a high growth potential, otherwise it's just a business as already pointed out by @sillysaurus3.

If tomorrow 250 people are queuing to get a drink from your bar, you won't be able to cater to their needs, nor the next day, opening a new brick-and-mortar business takes a lot of time.

A startup would be able to scale (after a couple of days / week) and fulfill the customers' needs.