second level cache in ORMs

This suggests that the second level cache in NHibernate is a bag of queried objects which may be requeried/reused at the C# side without a trip all the way back to the database! (The first level cache more mundanely holds a list of queries/transactions run that perhaps you do not want to rerun several times over.) The cache stuff can be a pain point as well as a blessing until you get used to it. You don't want to query the cache snapshot of an object you just updated for example. This gives more details on the second level cache for NHibernate's sister, Hibernate.