When you buy a new product like a car or a piece of electronic equipment, it usually comes with a warranty from the company that makes the product. The warranty is a kind of legal agreement. The company promises that their product will continue to work for a certain length of time. If it doesn't, the company will replace it or refund the customer's money.
In the U.S., products usually come with a "manufacturer's warranty", which is 90 days for a lot of products. But stores also try to sell their customers an "extended warranty", which costs extra but protects the product for a longer time.