Arbitrage
Buying an asset where it is cheaper and selling where it is dearer to capture the difference.
Arbitrage traders are why the same coin trades at nearly the same price on dozens of venues: any gap is closed within seconds by someone buying on the cheap venue and selling on the expensive one. Gaps persist only when arbitrage is blocked — by withdrawal suspensions, capital controls, or pools too shallow to trade at size — and a persistent gap is a signal of one of those.