subprogram or package compiled as a stand-alone unit (i.e. not embedded within any other unit) and added to the program library.

In PowerAda, one of five syntactic entities: a subprogram declaration, a package declaration, a generic declaration, a generic instantiation, or a subprogram body in the case where there is no corresponding subprogram declaration. As the name implies, a library unit resides in the Ada program library. The significance of library units is that they may be referenced by other independently compiled units. This reference may either be explicit (referenced via a with clause) or implicit (such as the reference of a package body to its specification).