A liquidity crisis happens when a company, bank, or country cannot pay their bills and debts, because they don't have enough money or liquid assets to cover their costs. For example, companies need cash to buy supplies and pay employees, but if they don't have enough cash, they won't be able to do those things. Banks also need cash to lend out to people, but if there's not enough cash, people won't be able to borrow money from them. When there's not enough money to go around, it's called a liquidity crisis.