Liquidity
Liquidity is how easily an asset can be bought or sold at a stable price; a liquid coin trades in size without moving.
A liquid market has many buyers and sellers close to the current price, so a large order barely moves it and the spread is tight. Trading volume and order-book depth are the usual measures.
Low liquidity is a risk on its own: prices jump on small orders, exits are costly, and a position can be hard to sell in a panic. On decentralised exchanges, liquidity is the money providers lock in a pool.