Unlike other symbols that have to line up in a particular combination on an active payline in order for you to win anything, a required number of scatter symbols simply have to show up on the reels within a single spin to trigger the free spins, mini-games, and whatever other win-boosting features the slot has to offer. Scatters also differ from other symbols in that they cannot be replaced by wild symbols.
These symbols are typically one of the highest paying symbols in a slot game too, and payouts awarded when you spin in a set number of scatter symbols are based on a multiple of the amount you wagered on the spin and not just the payline bet. On some slot games, the value of those multipliers can go up to a x100, x200 and even x500 your base game staked amount winning payout if all five scatter symbols appear.
Note that on more complex 5-reel video slots, scatter features will be game-specific – i.e. they will function differently, depending on the game. In some simpler slot games, scatter icons don’t unlock any additional features and just payout on a winning combination. You may not even find them at all on some three-reel slots.