GORM is half the reason why I use Grails as my default choice in implementing new projects. Using it just makes implementation of business logic a breeze. Working with a database becomes so easy.
GORM is Grails' object relational mapping (ORM) implementation, which sits on top of the very popular Hibernate framework. If you are familiar with Hibernate, then you can pick up GORM in an instant. Don't worry otherwise as GORM is straightforward and easy to learn.