A high roller is someone who gambles with large stakes. In casinos the term covers players whose total spend puts them among the operator's most valuable customers.
On GB online slots the room for very large stakes per spin is limited: the legal stake limit is £5 a spin for players aged 25 and over and £2 for those aged 18 to 24. High spending online therefore now comes from volume of play rather than individual spins, which still adds up quickly.
VIP and high-value customer schemes have been a focus of Gambling Commission enforcement. GB operators must check that spending is affordable and act when there are signs of harm. A higher stake does not change a game's odds or RTP; it only scales the result and the expected cost.