Although there isn't a single definition of a high roller, it generally refers to seasoned gamblers with a lot of cash and no reluctance to risk that money. They are known for enjoying the most desirable gaming status and using the best benefits at casinos.
If a player is in a land-based casino, they may be offered a private plane to carry them to the casino and a waiting limousine to take them anywhere they need to go. Their treats usually include penthouse apartments accompanied by the best meals and entertainment.
A high roller's lavish lifestyle is supported by physical casinos as part of their brand image, but online casinos are very different by their nature. Online casinos respond to this by providing high rollers with various benefits, including improved playing conditions, an extremely favorable selection of high roller bonuses, bigger deposit and withdrawal restrictions, negotiable comps, and similar things.
Whales and big money players are other terms used to describe high rollers. They typically have the largest bankrolls, a good grasp of the game they should play and how to play it, and the most money.
But you have to wager a lot to earn the title of a high roller. But it's not just about how much money you bring to the table; every high roller is recognized for placing large bets, making generous tips, and showing up to games in style.