Turbo spin, also called quick spin, is a setting that cuts the reel animation so each spin resolves faster. It is not allowed on GB-licensed online slots.
The Gambling Commission's game design rules from 31 October 2021 banned turbo and quick-spin features and set a minimum of 2.5 seconds per game cycle. Faster spins mean more spins an hour, so more money staked and a higher expected cost over the same time, which is what the rule was designed to stop.
Turbo options still appear in versions of games for other markets. On GB sites the spin speed is set by the game and cannot be shortened below the minimum. See game design rules.