Beta

Beta measures how much a stock's price tends to move relative to the overall market. A beta of 1 means the stock tends to move in line with the market, above 1 means it swings harder in both directions than the market does, and below 1 means it moves more gently.

Beta is calculated from a stock's own historical price movements, which makes it backward looking, past volatility relative to the market, not a forecast of future risk. It's commonly used as an input when estimating the return equity investors should require for holding a specific stock, a higher beta implying a higher required return, whether or not the business's actual underlying risk has moved in step with that number.