The term "options delta" is one of what are commonly called "the Greeks" in option trading, but understanding its significance can make a big difference to your trading decisions.In its simplest form, the delta is a number which describes the relationship between the movement in the price of the underlying financial instrument (stock, commodity, currency etc) and the option price that derives from it.
An example would be the "at-the-money" option. This refers to an option whose strike price is exactly the same as the current market price of the underlying. Whether we are talking call or put options, an at-the-money option always has a theoretical delta of 0.50 or 50 percent. The reason is, because from this 'at-the-money' position, the option contract has a 50/50 chance of expiring out-of-the-money. This is because in the future, the underlying will move one way or the other, up or down. It doesn't matter which way it goes, the odds are 50 percent, or 0.50 each way.
Now, the further away from the strike price the underlying moves, if it causes the option to go 'out-of-the-money', the less likelihood there is, that the option contract will be of any intrinsic value at expiry date. So the delta decreases. Conversely, if the underlying moves in your favour, thus making the option contract 'in-the-money' the more likelihood there is that option will expire with some intrinsic value. So the options delta increases, but only to a maximum of 1.0 or 100 percent which indicates certainty.