CORBA or Common Object Request Broker Architecture defines the APIs, communication protocol, and object/service information models to enable hetreogenous applications written in various languages running on various platforms to interoperate.
In a general sense CORBA "wraps" code written in another language, almost always C++, into a bundle containing additional information on the capabilities of the code inside, and how to call it. The resulting wrapped objects can then be called from other programs (or CORBA objects) over the network. In this sense CORBA can be considered as a machine-readable documentation format, similar to a header file but with considerably more information. These sorts of systems are generally referred to as Interface Definition Languages, or IDL's.
CORBA is more than just a language, platform neutral remote procedure call specification. It defines commonly needed services such as transactions and security.