Volatility

A statistical measure of the dispersion of returns for a security or market index, usually expressed as the annualized standard deviation of daily price changes. High volatility means large price swings in either direction, creating both opportunity and risk. Options prices are heavily influenced by volatility -- when volatility is low, options are cheap, and when it spikes, premiums expand dramatically, which is why the term "volatility crush" describes the rapid premium decline after an anticipated event passes.