This document discusses OWIN (Open Web Interface for .NET), which defines a standard interface between .NET web servers and web applications to decouple them. It aims to make .NET web development resemble HTTP, be asynchronous and composable. OWIN defines an "AppFunc" that takes an environment dictionary as input and returns a task. This allows multiple middleware components to process requests and responses in a pipeline. The document outlines the goals of OWIN and provides an overview of its key concepts like applications, middleware, hosts and the environment.