Faker.js is a popular JavaScript library used to generate fake data for testing and development purposes. It allows developers to create realistic-looking data such as names, addresses, phone numbers, and even entire user profiles. This is particularly useful for populating databases or creating mock applications without the need for real user information. The library is easy to use and can be integrated into various projects, whether they are front-end or back-end applications. By providing a wide range of data types and formats, Faker.js helps streamline the development process and ensures that applications can be tested effectively without compromising user privacy.