I tried searching for a simple explanation but couldnt find it. When to use DISCRIMINATOR and when to use SUBCLASS?

I assume you're talking about XML mapping files rather than annotations.

The discriminator is the column used to determine which subclass a row represents when using table-per-class-hierarchy inheritance mapping. The <discriminator> element specifies the details of this column (name, data type etc).

http://hibernate.org/hib_docs/reference ... criminator

The subclass element is used to specify the actual subclasses that are stored. You can specify the discriminator-value attribute for each <class> and <subclass> element to determine what value in the discriminator column hibernate will interpret as meaning that class.

http://hibernate.org/hib_docs/reference ... n-subclass