What is a whale in trading?

A trader whose stakes are big enough to move the price by themselves.

When a market jumps ten points on one trade, that was a whale surfacing. On real-money platforms whales move six figures; on Foresee it's whoever built the biggest Maura pile. Either way the mechanics are the same: big stake in, price shoves over.

Whales aren't cheating, they pay for the shove, because a market maker charges more per share the harder you push. If the whale is wrong, everyone who calmly took the other side gets paid. Watching what happens after a whale move is one of the fastest ways to learn how markets breathe.