Volatility

Volatility is a prediction that a stock will likely more. A high IV will mean that stocks has high probability that it will move one direction or another.

Debt spreads generally do better with increasing volatility.
Credit spreads generally do better with decreasing volatility.

Examples of debit spread
bull call spread
bear put spread
long call
long put
calendars

Examples of credit spread
bear call spread
bull put spread
short call
short put