Delta vs Vega

The rate of change of an option's price relative to a $1 change in the underlying asset price; ranges from 0 to +1 for calls and -1 to 0 for puts; ATM options have delta approximately ±0.5; delta is also used as a proxy for the probability that the option expires in-the-money.

The rate of change of an option's price relative to a 1% change in implied volatility; long options have positive vega (gain value when IV rises); short options have negative vega (lose value when IV rises); the primary risk in bought options around anticipated events.