Answer:
Polymorphism means that a variable of supertype can refer to a subtype object.
Explanation:
For example, in Python programming language, a function that accepts an iterable object uses the concept of polymorphism because that function can accept strings, lists, tuples as arguments.
It's easier to send the files that way because you don't have to attach them individually, and then your friend won't have to download them individually - they can just download the zip package and have all four right at their disposal.
