Linkage

Identifier names can refer to different identifiers in different scopes. An identifier declared in different scopes or in the same scope more than once can be made to refer to the same identifier or function by a process called "linkage." Linkage determines the portions of the program in which an identifier can be referenced (its "visibility"). There are three kinds of linkage: internal, external, and no linkage.

See also

Using extern to Specify Linkage