The CORBA is an architecture for distributed programming. The idea is that many processes on many different machines can operate on the same data objects regardless of where the objects and the processes actually are.
CORBA is not a program, it is a specification for how the above should be managed and/or implemented.
ILU, OmniORB, VisiBroker and the Oracle8iJServer are examples of CORBA implementations.
Actually, ILU is not a compliant CORBA implementation - it only implements the wire protocol part of CORBA. In particular, it's C and C++ language bindings are not CORBA compliant, which is why we're having all these problems with converting from ILU to OmniORB (which is CORBA compliant)
See also ORB, IDL, DocumentationForOmniMigration and AcronymSoup.
See also DocumentationForOmniMigration.