Strike Price
The predetermined price at which the underlying asset can be bought (call) or sold (put) when the option is exercised.
Explanation
Strike prices are set by the exchange at standard intervals. The choice of strike determines the moneyness, delta, premium, and risk profile of the option. Closer-to-the-money strikes have higher premiums but higher probability; farther OTM strikes are cheaper but less likely to profit.
Example
AAPL options are available at $5 strike intervals: $140, $145, $150, $155, $160, etc.