Beta is a measure of a stock's volatility in relation to the overall market. It indicates how much a stock's price typically moves in relation to the market as a whole. A beta of 1 means the stock moves in line with the market, while a beta greater than 1 indicates the stock is more volatile than the market and a beta less than 1 indicates the stock is less volatile. Investors use beta to assess risk and determine how a stock may perform in different market conditions.