Wikipedia says:
Method overriding, in object oriented programming, is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes.
In detail, when you have an object foo that has a void hello() function:
class foo {
virtual void hello(); // Code : printf("Hello!");
}
A child of foo, will also have a hello() function:
class bar : foo {
// no functions in here but yet, you can call
// bar.hello()
}
However, you may want to print "Hello Bar!" when hello() function is being called from a bar object. You can do this using override
class bar : foo {
virtual void hello() override; // Code : printf("Hello Bar!");
}