The mappings in a package are divided into two classes, external and internal. The symbols targeted by these different mappings are called external symbols and internal symbols of the package. Within a package, a name refers to one symbol or to none; if it does refer to a symbol, then it is either external or internal in that package, but not both. External symbols
are part of the package’s public interface to other packages. Symbols become external symbols of a given package if they have been exported from that package.
A symbol has the same name no matter what package it is present in, but it might be an external symbol of some packages and an internal symbol of others.