Polymorphism is a concept in object-oriented programming that means poly (many) morph (treat as one). Polymorphism means that a single object can be used in different ways, and many different objects can be used in the same way. It is an idea that allows an object to fulfill many roles.
A real-world example of polymorphism is a Blu-ray player. A Blu-ray player can play Blu-ray, DVD, and CDs. Blu-ray, DVDs and CDs are all played in different ways from each other, but all three media can be played, so they are polymorphically working in the Blu-ray player.
Devices of transportation can also be used as an example of polymorphism. You could use a car, bike, or walk from point A to point B, the internal functionality of these is all different, but all of them have the ability to get you where you want to go.