Liquidation means selling all the stuff in a store or business so that the owners can use the money they get to pay their bills and maybe start a new business someday.
Imagine you have a toy store, and you have lots of toys on the shelves that you haven't sold. You need money to pay the rent, the electricity, the people who work in the store, and the people who made the toys. But you don't have enough money because you haven't sold enough toys. So you decide to have a big sale where you sell all the toys at a big discount, so people will buy them and you can get enough money to pay your bills.
This big sale is called a liquidation sale because you are selling everything in your store, and turning it into liquid money (cash) that you can use to pay your bills. When people come into your store, they might see signs that say "everything must go!" or "50% off all toys!" That means you are trying to sell everything in the store, even the things that are normally very expensive, so that you can get enough money to pay what you owe.
Liquidation can happen to a store or a business for many reasons. Sometimes the owners have made bad decisions and can't pay their bills. Sometimes the store is going out of business because people aren't interested in buying their products anymore. Whatever the reason, liquidation means selling everything in a store or a business, so that the owners can get cash and hopefully move on to something new.