Since calls puts both increase in value as volatility increases, if you are long either you are long vega. Vega is highest for ATM options and decreases as options move in and out of the money and ATM options are therefore the most sensitive to changes in implied volatility.
A long option position will have a positive vega. For example, if you are long an option and volatility goes up, your position value increases even if underlying asset is flat. A short option position has a negative vega. As volatility goes up with underlying asset remaining flat, the cost to close the short position increases thus reducing position value. If a position has positive vega then you want the volatility to increase resulting in an increase in position value. If a position has negative vega then you want the volatility to decrease in order to see an increase in position value.

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