Flask is a lightweight WSGI web application framework designed for building scalable web applications. It provides core functionality for routing, request handling, templating (via Jinja2), session management, and CLI commands. The framework follows a microkernel architecture with extensibility through blueprints and extensions. Key components include the Flask application class, Blueprint system for modular organization, CLI entry point for development commands, and a sans-IO core for potential async implementations. Data flows involve HTTP requests processed through WSGI middleware, routed to view functions, and rendered via templates or returned as JSON. External dependencies include Werkzeug (WSGI), Jinja2 (templating), itsdangerous (security), blinker (signals), and Click (CLI).