EAV is Magento’s core database modeling system designed to offer high flexibility. Instead of using a traditional flat table where every product attribute (color, size, weight) gets its own column, EAV splits data across multiple tables: the Entity (e.g., a specific product), the Attribute (e.g., “color”), and the Value (e.g., “blue”). This allows store owners to add custom attributes on the fly without needing database schema updates.
Official Documentation: EAV and Attributes