A set of codes (libraries) that fits into a framework to handle a particular task. It cannot perform the task by itself.
If a module is so important and widely used, eventually it will be included as a part of the framework.
Typical web application modules’ tasks are:
- User authentication (login, signup, restricted content).
- Connection to other software like databases and web servers.
- URL parser.
- Apps of a mobile phone. You can download them to enhance your phone’s experience. Many widely used apps (eg. Photos) now come pre-installed.
- Too many of them. They are often stored in repositories and managed by frameworks’ module managers.