Starburst is built around a single, clean mechanic that’s made it the most widely distributed slot in online casino history. Across a 5×3 grid with 10 paylines that pay both left-to-right and right-to-left, the entire bonus structure rests on one feature: when a wild lands on reels 2, 3, or 4, it expands to fill the whole reel and triggers a free respin, which can chain up to three times if further wilds appear on the same reels. There’s no separate free spins round, no scatter symbols, and no multiplier accumulation to track – just that one trigger, repeated. Low volatility and a modest 500x max win mean Starburst isn’t designed to produce dramatic swings; it’s built for frequent, steady action across an extended session. That predictability, combined with its simplicity and colourful space-gem visuals, is exactly why it’s become the default welcome-bonus and wagering-requirement slot at so many online casinos – it’s easy to understand within seconds of the first spin.