A very simple polymorphic example of what you are saying would be to have a namespace (or in other langs, a class) that declares a function - for example, something to print out text. It's generic and only takes an argument, prints it.
It becomes polymorphic when you have others like 'English', 'Spanish', etc extend the namespace with little sub functions. So like, you could have a func 'helloworld()' in your main namespace, which accepts a string argument/parameter. The English extension would have the same helloworld(), and it would send the text "Hello World" to your main namespace. The Spanish version's helloworld function would send "Hola Mundo" to it.
This is polymorphic because the main namespace / class has a general purpose that is altered by those extensions.