The option strike price is the fixed price per share at which a stock option can be exercised to acquire common stock. It is set at grant date and unchanged for the life of the option, required by IRC Section 409A to equal the fair market value of common stock at grant date (set by the most recent 409A valuation), with significant tax penalties for the recipient if granted below FMV. It is the structural anchor of every option grant and the variable that determines the eventual cash outlay and bargain element at exercise.
The strike-price mechanics: