An options chain is the menu of every contract available on a stock - organized by expiration date and, within each, by strike price. Calls are usually on one side, puts on the other, with the current stock price near the middle.

The columns that matter

For each strike you will see the bid (what buyers will pay), the ask (what sellers want), the last traded price, volume (contracts traded today), and open interest (contracts still open). The gap between bid and ask is the spread - your immediate cost to get in and out. Tight spreads mean liquidity; wide spreads mean you are paying a toll on every trade.

Volume vs. open interest

These two get confused constantly. Volume is how many contracts changed hands today; open interest is how many contracts exist and have not been closed. High volume means active trading right now; high open interest means a lot of positioning is parked at that strike - which can matter for how the stock behaves near it.

The chain is not a wall of noise. It is a map of where liquidity and positioning actually sit.

What to focus on

For short-dated trading on a liquid product like SPY, focus on: the expiration you want, strikes near the money (where delta is meaningful), the spread (tight is non-negotiable), and enough volume to fill without slippage. The rest is detail. Reading the chain well is not about memorizing every column - it is about quickly finding a contract you can enter and exit cleanly.