Polymorphism is a greek word when we break this word into two parts like poly and morph it means poly says "Many" and morph means "meanings" , so one form having different meanings are said to be polymorphism.
Eg. Break system in vehicles.
Overriding in Java:--
See if the two methods are there one is parent and other is child then child able to access the methods arguments through inheritance but some of the arguments not satisfied by the child class then it will make some changes by its own way and will adding new argumets which is suitable for child class that process is nothing but overriding.