What is market liquidity?

When investing or trading into the stock/futures/crypto/options/etc. market, one thing you will see is the market liquidity. It is a market's feature that allows an individual or firm to quickly purchase or sell an asset without causing a change in the asset's price. That is achieved by other people already looking for the same asset at that price (the market price). Liquidity is all about the trade-off between how fast an asset can be bought/sold and for what price. Liquid markets are ones that have buy and sell side close in price, so that a person can buy and sell an asset for approximately the same price.

Of course, the most liquid asset is none other than money (cash) itself. It can instantly be sold for goods and services, and does not lose value in the process.