It's common to hear about Odoo modules and applications. But what exactly is the difference between them? Modules are building blocks of Odoo applications. A module can add or modify Odoo features. It is supported by a directory containing a manifest or descriptor file (named __openerp__.py) and the remaining files that implement its features. Sometimes, modules can also be referred to as "add-ons." Applications are not different from regular modules, but functionally, they provide a central feature, around which other modules add features or options. They provide the core elements for a functional area, such as accounting or HR, around which other modules add features. Because of this, they are highlighted in the Odoo Apps menu.