Vega

A first-order Greek that measures the sensitivity of an option's price to a one-percentage-point change in implied volatility of the underlying asset. Vega is always expressed as a positive number for both calls and puts, since higher implied volatility increases the probability of the option finishing in the money and therefore raises its premium. Long options positions have positive vega exposure (benefit from rising volatility) while short options positions have negative vega (benefit from falling volatility).