What is a member of a class that cannot be externally used?

There are several different keyWords in .Net languages that are used to define the "accessability" of a member or method. For example, in C#, the "private" keyWord is used to indicate that this member or method cannot be accessed by any instance of the class, nor by any class that inherits from the class. "Protected" is similar to "private" but allows inherited classes to acces those members. "Internal" allows access to those members freely to any class that is also declared in the same assembly.