Portfolio & riskAdvanced
Value at Risk is a loss threshold for a portfolio over a set horizon, estimated so that losses are expected to exceed it only with a small stated probability, such as 5%. A 95% one-day VaR of HK$20,000, for example, means a loss larger than HK$20,000 is expected on about 1 day in 20 under the model's assumptions.
Options & futuresAdvanced
Vega is the option Greek that estimates how much an option's price changes for a one percentage point (one volatility point) change in implied volatility, holding other inputs constant. Both calls and puts have positive vega when bought.
Portfolio & riskBeginner
Volatility measures how widely an asset's returns vary around their average, most often as the standard deviation of returns, usually quoted as an annualized percentage. Higher volatility means larger price swings in both directions, not a particular direction.