Differential between option strike prices. For example, strike interval can be $2.50 and available strikes $35, $37.50, $40, $42.50, $45.

For exchange-traded options strike price interval is typically standardized and decided by the exchange, based mainly on underlying price and liquidity or popularity of the underlying.

Typical strike intervals for US exchange-traded stock options are $1, $2.50, $5, and $10.