Positive feedback loop
Also said as Snowballing, Rich get richer, Reinforcing loop
A loop where doing well makes you better at doing well: winning gets you the thing that helps you win. Positive here means it amplifies, not that it is good.
It gives a game a shape, because a small lead becomes a decision and the game ends instead of dragging on. Left unchecked, the winner is settled long before the last hour, which everyone else has to sit through anyway.
Say it
“Kills give too much gold, so the first fight decides the whole match. Cut the kill bounty by half and pay it to the whole team instead of the killer.”
Where you’ve seen it
Monopoly: owning property pays rent, which buys more property. The game is often decided an hour before it finishes. In League of Legends, a kill gives gold, gold buys items, and items get more kills.
Not to be confused with negative feedback loop
A positive loop widens the gap between players. A negative loop closes it. The words say nothing about which is pleasant.