In terms of Java, when someone asks:
what is polymorphism?
Would overloading or overriding be
The term overloading refers to having multiple versions of something with the same name, usually methods with different parameter lists
public int DoSomething(int objectId) { ... }
public int DoSomething(string objectName) { ... }
So these functions might do the same thing but you have the option to call it with an ID, or a name. Has nothing to do with inheritance, abstract classes, etc.
Overriding usually refers to polymorphism, as you described in your question