Jest is an open-source JavaScript testing framework developed by Meta, designed to ensure the correctness of JavaScript codebases. It is commonly used for testing React applications, but it can also be utilized for testing other JavaScript projects, including Node.js applications. Jest offers a delightful developer experience with zero configuration needed, and it includes features such as a built-in test runner, assertion library, and support for mocking and spies. It also provides powerful tools like snapshot testing and parallel test execution to optimize testing performance.