Options don’t last forever; they have an expiration date. If an option is not closed out or exercised prior to its expiration date, it ceases to exist as a financial instrument.

Exercising an option means the holder is using their right to buy (for call options) or sell (for put options) the underlying asset at the specified strike price. In general, options are exercised when they are In-The-Money.

There are two main exercise styles for options:

1. **American Style**: These options can be exercised any time up to and including the expiration date. Most exchange-traded options are American style.

2. **European Style**: These options can only be exercised on the expiration date itself. 

– Reference: [Investopedia: Option Expiration and Exercise](https://www.investopedia.com/terms/e/exercise.asp)

Understanding these key elements of option contracts will provide you with the necessary foundation to explore more complex options strategies and trading methods. Always remember that trading in options involves risk and requires careful planning and thorough understanding.