The Beta of a stock represents the tendency of a security or stock to respond to swings in the market (generally the the S&P 500), it’s a measurement of the relationship between the price of a stock and the movement of the whole market.
For example: If a stock has a beta of 1.5, it means that for every 1 point move in the stock market, the stock moves approximately 1.5 points.
Lower beta stocks have less volatility and do not carry as much risk, but generally provide less opportunity for a higher return on market swings.
With all that being said, BETA is ok for larger cap stocks, but not for more volatile smaller cap stocks as they tend to swing on news, catalysts, and other factors more often that larger cap stocks.
Also referred to as the Beta Coefficient.