PHP 7.3 reaches end of support in December 2021 and Adobe Commerce 2.3.x reaches end of support in April 2022. We strongly recommend planning your upgrade now to Adobe Commerce 2.4.x and PHP 7.4.x to help maintain PCI compliance.

Magento_Eav

Magento\EAV stands for Entity-Attribute-Value. The purpose of Magento\Eav module is to make entities configurable/extendable by admin user.