Coefficient measuring a stock's relative volatility. The beta is a covariance of the stock in relation to the rest of the stock market. The Standard & Poor's 500 Stock Index has a beta coefficient of 1. Any stock with a higher beta is more volatile than the market, and any stock with a lower beta can be expected to rise and fall more slowly than the market. A conservative investor whose main concern is preservation of capital should focus on stocks with low betas, whereas one willing to take high risks in an effort to earn high rewards should look for high-beta stocks.