Which Option ‘Greek’ Measures the Sensitivity to Volatility Changes?

Vega is the option Greek that measures the sensitivity of an option's price to a 1% change in the implied volatility of the underlying asset. A high Vega means the option's price will change significantly if the market's expectation of future price swings changes.

Vega is always positive for both call and put options, meaning an increase in volatility increases the premium.