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Beta is a type of statistical measure that helps to assess risk in stocks and the volatility of stocks with relation to the overall market. It helps investors decide whether he/she wants to go for riskier stocks that are highly correlated to the market, which are indicated as beta being above 1, or less volatile which is indicated as beta below 1.
Beta is the key factor used in the CAPM(Capital Asset Price Model) which is a model that helps in measuring the return of stock. The volatility of the stocks and the risk associated with it can be judged by calculating beta. When stocks generally move in the same direction with that of the market and vise versa, the beta value is said to be positive. For example, if the beta value is 1.2 and the market is expected to move up 9%, then the stock would move up by 10.8%(1.2*9).