What is a “maiden” in horse racing?
A maiden in horse racing is not held captive in a tower by an unspeakable monster. It is simply a horse that has never won a race.
The term applies to both males and females, so it’s not gender improper to say a colt is still a maiden.
Once a horse wins a race, it still may be referred to by its level of achievement. A horse that is running in claiming races is often referred to as a “claimer,” and a horse that has beaten top competition might be referred to as a “stakes winner,” for instance.