The difference between the underlying security's current market price and the option's strike price represents the amount of profit per share gained upon the exercise or the sale of the option. This is true for options that are in the money; the maximum amount that can be lost is the premium paid.
Also known as the "exercise price."
Strike prices are one of the key determinants of the premium, which represents the market value of an options contract. Other determinants include the time until expiration, the volatility of the underlying security and prevailing interest rates. Strike prices are established when a contract is first written. Most strike prices are in increments of $2.50 and $5.
Investment dictionary. Academic. 2012.