What is the difference between a class and a module?
Modules are collections of methods and constants. They cannot generate instances. Classes may generate instances (objects), and have per-instance state (instance variables). Modules may be mixed in to classes and other modules. The mixed-in module’s constants and methods blend into that class’s own, augmenting the class’s functionality. Classes, however, cannot be mixed in to anything. A class may inherit from another class, but not from a module. A module may not inherit from anything.
