An ancillary product is a product which is purchased or licensed on a restricted use basis in conjunction with the principal
manufacturer's product being acquired (e.g., may be used only in combination or by educational institutions for research use). For instance, a third party software which is licensed to licensor and furnished to licensee on a limited use basis subject to the license restriction that it may only be used in conjunction with the licensed software.
Source: www. PnpPsgGlossary.doc