The Open Web Interface for .NET (OWIN) is a standard that defines an interface between .NET servers and web applications. Katana is an implementation of OWIN by the .Net foundation. Kestrel is a lightweight cross-platform web server that supports .NET Core and runs on multiple platforms such as Linux, macOS, and Windows.
A lifecycle is a series of components, events, and stages that process a request or respond to user interaction. The framework lifecycle offers extension points and hooks into these components so that you can customize the final output. asp.net core provides a framework lifecycle to process requests.