As a proxy for probability
Main article:
Moneyness
The (absolute value of) Delta is close to, but not identical with, the percent
moneyness of an option, i.e., the
implied probability that the option will expire
in-the-money (if the market moves under
Brownian motion in the
risk-neutral measure).
[5] For this reason some option traders use the absolute value of delta as an approximation for percent moneyness. For example, if an
out-of-the-money call option has a delta of 0.15, the trader might estimate that the option has approximately a 15% chance of expiring in-the-money. Similarly, if a put contract has a delta of −0.25, the trader might expect the option to have a 25% probability of expiring in-the-money.
At-the-money calls and puts have a delta of approximately 0.5 and −0.5 respectively with a slight bias towards higher deltas for ATM calls. The actual probability of an option finishing in the money is its
dual delta, which is the first derivative of option price with respect to strike.
[6]
daar ga ik niet onnozel over doen. Hopelijk gunnen jullie mij ook mijn vreugde. 
Mij hoor je iig niet klagen. 't Was over het algemeen een mooi groen dagje.
