In section 10.4 (Hull's 9th - global), there are two paragraphs on expiration dates for options. I have a few questions as below. What does the Jan, Feb, Mar cycles mean? What role does it play in trading? Does it means usually an option has 3-month term? The text talks about the situation where the expiration date for the current month has not yet been reached and also the opposite situation. Is there a reason why such rule is needed and/or how such rule is derived? Thank you!