What does hbm in the NHibernate mapping files stand for?

When using NHibernate you need to provide some mapping files with the name .hbm.xml which are used to define the mapping from POCO to the databa开发者_如何学编程se. But what does the hbm stand for? Is it an abbreviation for something or was it created by pure chance?

NHibernate was a spin off from Hibernate a Java application, as dotjoe said

"h i b ernate m apping"

Cheers