Implied volatility
The volatility input that makes a pricing model match an option's market price. It reflects the size of expected moves and says nothing about direction.
Implied volatility is backed out of option prices instead of being measured from past prices, and it is quoted as an annualized percentage. When demand for options rises ahead of an earnings report or other event, option prices and IV rise together, and once the event passes IV usually falls.
IV differs across strikes and expirations, patterns known as skew and term structure. A common rough conversion divides annualized IV by the square root of 252 to estimate a one-day move of one standard deviation.
Illustrative example (hypothetical numbers, not a real trade): a stock at $100 has options priced at an IV of 32%. Dividing 32% by the square root of 252, about 15.9, gives roughly 2.0%, so the options imply a one-day move of about $2 in either direction at one standard deviation.