Vega is the option's price change for a one-percentage-point change in implied volatility. Debit structures and straddles are long vega; credit spreads and condors are short vega, gaining when volatility falls or stays overpriced.
Vega is largest for at-the-money strikes and longer expirations, which is why LEAPS are volatility positions whether the holder intends it or not. Short-vega structures are screened for rich premium at entry because their edge is the volatility they sell; a portfolio-level vega cap bounds how much of the book one volatility shock can hit at once.