A bonus feature is anything in a slot that goes beyond a standard spin and payout. Early mechanical machines had none — a spin either paid or it did not — but modern games are designed around them.
Common examples include free spins, multipliers, cascading reels, sticky, expanding or stacked wilds, respins and pick-me mini-games. Each title sets its own triggers: landing three or more scatters is the classic route, but features can also start at random, or be bought directly where the market allows it.
For operators, features shape how a game feels and pays. In high-volatility titles, a large share of the return often comes from the bonus round. Grouping games by feature type in the lobby, and checking local rules on bonus-buy options, helps players find what they enjoy while keeping the catalogue compliant.