An addon module is a directory containing the files that implement some Odoo features. It can add new features or modify existing ones.
The addon module directory must contain a manifest, or descriptor file, named __manifest__.py, plus the other module files.
Some module addons are featured as Apps. These represent applications available for Odoo, and usually add their own top-level menu item. They provide the core elements for a functional area, such as CRM or HR. Because of this, they are highlighted in the Odoo Apps menu. On the other hand, non-App module addons are expected to add features to these Apps.
If your module adds new or major functionality to Odoo, it probably should be an App. If the module just makes changes to the functionality of an existing App, it probably should be a regular addon module. We will show you this in the next section...
