ORM stands for Object Relational Mapping. It’s a programming technique used to convert different types of data to Objects and vice versa.
In Magento, ORM is shown as Model (based on Zend Framework’s Zend_Db_Adapter), which further breaks down to two types of Models.
First is the “simple” i.e. Regular Models which is nothing but flat table or our regular table structure.
Second Model is EAV (Entity Attribute Value), which is quite complicated and expensive to query.