Module (Craft CMS/Yii)
A module in Craft CMS is a self-contained set of code that provides specific functionality and, unlike a plugin, is stored and managed inside of the Craft CMS project. Modules are similar to Craft CMS plugins but are typically more tightly coupled with the specific project.
Modules are based on Yii’s Modules
You can create a new module using the Craft Generator tool, available in Craft CMS 4+.