The price fixed in the contract at which the option can be exercised (to buy or to sell), regardless of the market price.
What this price decides
The Strike Price (Strike Price) is the price agreed in the contract. The call holder has the right to buy the stock at it, the put holder the right to sell at it, whatever the market price. Every option chain is simply a list of strikes around the stock price, each with its own price, liquidity and Greeks.
How it classifies contracts
Where the strike sits relative to the market price splits contracts into three kinds: in the money when the strike carries intrinsic value, at the money when it is roughly equal to the market price, and out of the money when it has no intrinsic value. The kind sets how the whole contract behaves: its delta, gamma, price and sensitivity to time.
Choosing the strike is choosing the leverage
A strike near the price costs more and moves faster. A far out-of-the-money strike is cheap, but it is less likely to be reached and Theta eats it relatively faster. The difference between traders is often not the direction but which strike they bought.
Hypothetical example
A stock at $150. A call with a $145 strike is in the money: its intrinsic value is $5, plus some time value. A contract with a $150 strike is at the money: all of its value is time value and its gamma is highest. A contract with an $165 strike is out of the money: cheap, and it pays at expiration only if the stock passes $165 plus what was paid for it.
Common mistake
Judging a contract by its price alone: "this is cheap". Cheap here reflects a far strike and a short expiry · that is, a lower probability, not a hidden opportunity.
Where to see it on the platform
The options chain on the platform shows strikes as rows. The Call Wall and Put Wall on the Gamma board are the strikes where the largest positioning in contracts piles up.
