A compilation unit that is a specification, not a body. It is part of an Ada library, displayed as a graphical icon in AdaVision. ( See also Compilation unit.)

a child of its parent unit

A library unit is a separately compiled program unit, and is always a package, subprogram, or generic unit. Library units may have other (logically nested) library units as children, and may have other program units physically nested within them. A root library unit, together with its children and grandchildren and so on, form a subsystem. (23)

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).