Option contracts on the same class having the same strike price and expiration month. For example, all XYZ May 60 calls constitute a series.
See Also:
Option: A contract that gives the owner the right, but not the obligation, to buy or sell a particular asset (the underlying stock) at a fixed price (the strike price) for a specific period of time (until expiration) . The contract also obligates the writer to meet the terms of delivery if the contract right is exercised by the owner.
Series: All option contracts of the same class that also have the same unit of trade, expiration date and strike price.