eCos is designed to be the component framework for the embedded systems industry. An eCos release consists of a number of different packages including the kernel, the C library, and a uITRON compatibility layer. All the packages that go into such a release and the associated documentation constitute the core system, and the license describes this using the term "Original Code".

Another way of looking at this is from a purely practical perspective. At the end of the day building an application involves linking together some application-specific object files with some libraries. The current eCos build system will produce a library libtarget.a, containing all the packages that the user has selected. All the source code that goes into the building of this library is part of the core system and is covered by the eCos public license. Anything which goes into the application-specific object files is not part of the core system and is not covered by the public license. Note that this is not a legally binding definition - in particular you cannot get around the public license simply by copying bits of eCos sources and making them part of your application code.