Definition of Expiry Date:
First of all, let's be clear that "Expiry" and "Expiration" mean the same thing. The expiry date of a call or put option is the date that the option expires. In the U.S., all options used to have an expiry date of the third (3rd) Friday of each month. However, over the last few years the option exchanges have begun issuing call and put options that have a weekly expiry. The weekly expirations are not for every option, but just the most actively traded indices, stocks, and ETFs.
When you have call or put options in your brokerage account that are close to the expiry date, you will typically receive email reminders from the broker or you might receive alerts when you login to your brokerage account. These emails or alerts will begin at the first of the month of the expiry date, and then again on the Monday before the expiry date, and then again finally on the morning of the expiry date.
On or before the expiry date, if your option is in the money, you must either sell your option or exercise it by this date. If you have a call option, you would buy the stock at the strike price. If you have a put option, you would sell the stock at the strike price. If the option is "out of the money" then the option just expires worthless and drops off of your account and you lose all of the money that you spent on the option.
Here are the top 10 option concepts you should understand before making your first real trade: