Action Pack is a framework for handling and responding to web requests. It
provides mechanisms for routing (mapping request URLs to actions), defining
controllers that implement actions, and generating responses by rendering views,
which are templates of various formats. In short, Action Pack provides the view
and controller layers in the MVC paradigm.

It consists of several modules:
- Action Dispatch, which parses information about the web request, handles
  routing as defined by the user, and does advanced processing related to HTTP
  such as MIME-type negotiation, decoding parameters in POST, PATCH, or PUT
  bodies, handling HTTP caching logic, cookies and sessions.
- Action Controller, which provides a base controller class that can be
  subclassed to implement filters and actions to handle requests. The result of
  an action is typically content generated from views.

With the Ruby on Rails framework, users only directly interface with the Action
Controller module. Necessary Action Dispatch functionality is activated by
default and Action View rendering is implicitly triggered by Action Controller.
However, these modules are designed to function on their own and can be used
outside of Rails.

See also: https://rubyonrails.org/