Polymorphism, abstract classes, pointers, references

Give short definitions of polymorphism, an abstract class, a pointer and a reference in C++.

Polymorphism: one interface, many behaviours, e.g. a base reference calling the right override at run time (or templates and overloading at compile time). Abstract class: has at least one pure virtual function, so it cannot be instantiated. Pointer: a variable holding an address; it can be null, reseated and do arithmetic. Reference: an alias bound to an object at initialisation, never null or reseated.