Definitions for "open class"
a class to which new fields or methods can be added without editing the class directly
A class that may have subclasses that are not explicitly defined in the same library. The opposite of an open class is a sealed class.
An optional 2 age class just for fun (no points)
Keywords:  compete, horses, races, older, four
Horses, generally four years of age and older, which compete in races open to the most well-performed horses.