From UrbanCode website: 

"The Coarse Grained Container Managed Entity Bean idiom is identical to the Coarse Grained Entity Bean except that the container manages the [persistence]. This allows the container to make optimizations. This also frees developers from having to write persistence code that is often not portable across data sources. 

http://www.urbancode.com/projects/ejbbenchmark/idioms.jsp

See Also UrbanCode, EjbBenchmark , EjbIdioms