"warranty" and "guarantee" are often used interchangeably, even though they have somewhat different meanings. A "warranty" is written and has a time limit. It offers to rectify a service, or repair or replace a product. A "guarantee" is a formal assurance that a product or service will be of a certain level of quality. It typically has no time limit. Here are examples of usage: "I told him that my showing up at the movies on time was guaranteed." "After the refrigerator stopped working, the couple carefully read the manufacturer's warranty."