A feature board is the lit-up display above or beside a fruit machine's reels, showing a trail or ladder of features: cash prizes, nudges, extra spins, and bonus games. Symbols or numbers won on the reels move you along it.
Progress on the board can lead to features such as a "reel bonus" or a cash ladder, often with a gamble step where you can risk a prize to climb higher or collect. The board makes play feel like a journey with goals, which is part of the appeal of the British fruit machine.
As with nudges and holds, the feature board is built into the machine's maths, so the overall return is set by its design, whatever happens on the trail. Online fruit-machine-style slots often recreate the feature board on screen.