What is steam in betting?

A price moving fast in one direction because informed money is piling in.

When a percent climbs 5, 8, 12 points in minutes, that's steam, the market absorbing news or sharp action before you've even seen the headline. Chasing steam (betting the direction it's moving) is a whole strategy; so is fading it when you think the move overshot.

Steam is why prediction markets beat news feeds: the price often moves before the push notification arrives, because somebody somewhere always knows first and bets it.