Liquidity

Liquidity is the ease with which an asset can be bought or sold quickly without causing a large change in its price. A liquid market has many active buyers and sellers, narrow bid-ask spreads, and substantial depth, so orders execute close to the quoted price. An illiquid market has few participants, wider spreads, and thin depth, so trades can move the price sharply.

Liquidity is a property of the market at a point in time, not a fixed feature of an asset. A common misconception is conflating liquidity with trading volume; high past volume does not guarantee that liquidity is available right now.