Platform independant usually means not dependant on OS, but sometimes it means not dependant on OS or processor (which usually means it only uses the standard library, like a basic ''hello world'' program in C). I don''t think it is often used to mean it can run on any processor but only one OS (that usually only happens with linux, so they''ll just say it is for linux).

AFAIK there aren''t any really specific terms. Maybe we should start calling processor independence ''architecture independance'' since thats really what it usually means, and then platform independence could mean only not dependant on the OS.