In a margin trade (one using borrowed money to cause greater volatility in the trade), the liquidation price is the price of an asset that triggers a margin call.

A margin call is when the money put down to secure the borrowed money for a margin trade has been completely eaten up by the trade moving against you.

For example, say you go long on ETH at $200 with 20x leverage (5% margin). You put down $10 0 as margin, buying you $2000 of ETH (or 10 ETH). The liquidation price would be when the price of ETH drops by 5%, which would be $190. At that point your $100 margin would be completely lost, and your trade would be closed.