What do you mean by internal linking and external linking in c++?

What do you mean by internal linking and external linking in c++?

[This interview question is related to questions on "translation unit" and "storage classes"]

A symbol is said to be linked internally when it can be accessed only from with-in the scope of a single translation unit. By external linking a symbol can be accessed from other translation units as well. This linkage can be controlled by using static and extern keywords.