If something's at stake, it's at risk of being lost. When you play the board game Monopoly, there's nothing at stake except your pile of colorful Monopoly money.
When nothing's at stake, you have nothing to lose — but when there's a lot at stake, you're taking a big risk. In a high-stakes poker game, there might be thousands of dollars at stake, and when you perform in a talent show, you may believe your dignity and reputation are at stake. The idiom comes from an old 16th-century gambling term where to "stake" meant to place down a sum of money as a pledge or bet on the outcome of an event.