Vega
The option Greek measuring the contract price's sensitivity to a change in implied volatility. High vega means IV strongly affects the option value.
Definition
Vega measures the sensitivity of an option price to a change in implied volatility — when IV rises, premiums usually rise (positive vega for a long option), and when IV falls they shrink. Vega matters especially around events (earnings, central bank decisions).
Example
You buy a straddle before NFP when IV is already high. After the release IV drops (a crush): even with a price move, your long can lose money because the fall in IV and theta outweigh it. Vega explains that mechanism.
Anti-example / common mistake
Looking only at delta and ignoring that you are long or short volatility. Buying options “because there is news coming” at exactly the moment when vega is already expensive.
Poland / product
On a classic listed option chain, vega comes from the model and from market quotes. On the “options” some CFD brokers offer, do not assume the same Greeks apply — read the KID. Before selling premium: know whether you are short vega, and define a maximum loss in PLN of no more than 1R.