Deliberately enigmatic or ambiguous question requiring a thoughtful and often witty answer.
The riddle is a form of guessing game that has been a part of the folklore of most cultures from ancient times. Western scholars generally recognize two main kinds of riddle: the descriptive riddle, usually describing an animal, person, plant, or object in an intentionally enigmatic manner (thus an egg is "a little white house without door or window"); and the shrewd or witty question. A classical Greek example of the latter type is "What is the strongest of all things?"
"Love: iron is strong, but the blacksmith is stronger, and love can subdue the blacksmith."