Flask is a lightweight and flexible open-source web framework for Python, designed for building web applications quickly and with minimal overhead. It is based on WSGI (Web Server Gateway Interface) and provides developers with the freedom to choose their tools and libraries, making it highly customizable. Flask is known for its simplicity, ease of use, and scalability for both small and large applications.

Features of Flask:

• Minimalistic and lightweight, offering only essential tools to get started.
• Extensible with a wide range of third-party extensions for features like authentication, database management, and form handling.
• Built-in development server and debugger for fast testing and debugging.
• RESTful request handling for building APIs and web services.
• Jinja2 templating engine for rendering HTML dynamically.
• Routing and URL mapping for defining application endpoints.
• Supports both synchronous and asynchronous programming.
• Comprehensive documentation and active community support.

Run these commands:
$ pip install Flask
$ python -m flask run

Disclaimer: Flask is open-source software provided under the BSD License. It is offered "as is," without any warranty, express or implied. Users are responsible for ensuring the ethical and legal use of Flask in their projects.