Oversimplifying for this context: subclassing is reusing the implementation of a parent class, subtyping is when a type can be substituted for a (parent) class for some given functionality. It's confusing because it's not always easy to explain what constitutes "substitute", e.g. see "Liskov Substitution Principle". In some languages there might not be any class or interface relationship between subclasses - they just have the right functions that do the right things.