Object-relational mapping (aka ORM, O/RM, and O/R mapping) is a programming technique for converting data between incompatible type systems in relational databases and object-oriented programming languages. This creates, in effect, a "virtual object database" which can be used from within the programming language. There are both free and commercial packages available that perform object-relational mapping, although some programmers opt to create their own ORM tools.
Reference:
http://en.wikipedia.org/wiki/Object-relational_mapping
Reference:
http://en.wikipedia.org/wiki/Object-relational_mapping
