Flask is a lightweight web framework for Python that provides the essential tools to create web applications and APIs. Known for its simplicity and flexibility, Flask is often used for small to medium-sized projects, but it can also scale to handle complex applications. It supports extensions for adding features such as database integration, authentication, and more, without imposing strict architectural patterns. Flask follows a modular design, allowing developers to build applications with fine-grained control. Its minimalistic approach makes it a popular choice among developers who value simplicity and customization.