XPIDL stands for XP Interface Description Language. It is a specification for XPCOM which is a cross platform adapter description language. An adapter description language is used to describe an adapter which unrelated with its machine language. The description of the adapter can use specialized tools to handle automatoc generation of language that is unrelated to the adapter's specifications. Typically XPIDL is frequentle frequently used to generate C++ header files and typelib information.