Term life insurance is temporary, providing life insurance protection for a specific period of time, usually for a period of 10, 15, 20 or 30 years, or until you reach age 65.
Whole life insurance provide lifetime life insurance protection and does not expire.
Some life insurance policies do expire (like term life) because that is what they are created to do - to last for a temporary timeframe. That's one main reason term life insurance costs a lot less than permanent life insurance.
Some people have temporary life insurance needs; such as, to provide protection until the home mortgage is paid off, or their kids are grown up and out of college. And, term life is the most affordable way to provide this protection.
Keep in mind, many term life policies have an option available that allows the insured to convert the term life insurance into a permanent life insurance policy so the coverage does not expire.
Here's how you can learn more about whole life insurance versus term life insurance.