The word polymorph literally means "many forms". In software development, polymorphism allows us to use a common interface to perform different tasks. This means we can dynamically (i.e. at runtime through user input, files, etc.) change what our code does, without using large numbers of 'if' statements.
In this video I use initializer lists in the class constructors, which I haven't used in previous videos. I wanted to point out that this is just another (preferred) way to initialize a class' members, as opposed to assigning them in the constructor's body.