Dictionary.com defines open-ended as "allowing for a spontaneous, unstructured response".
Open ended questions are a big deal for preschoolers. Give it a try. Ask a little person you know "what is your favorite store?" And then ask why it's their favorite. They may stare at you blankly or give you a completely nonsensical even fantasy-like answer. It takes a lot to think of the question you asked and then to think of what the answer might be. Particularly because preschoolers are still at the stage of wanting to make you happy with the right answer. So not only are they trying to think of the name of a store, trying to figure out whether or not they like it, they are also looking at you and trying to determine what answer will make you happy.
Contrast that with "Do you like Wal-Mart or Publix?" You'll get your answer a whole lot quicker but if you move on to the why question which is open ended you are back at the blank stare or nonsensical answer.
It reminds me of a scene in Elmo Loves You. A little girl says to Grover, "I love you!" Grover says, "Really, what is love?" She says, "Huh?" and kind of looks away. She does eventually answer. It's not that she doesn't know what love is or that she did not mean it. She just doesn't know how to explain it.
So anyway, it's a big deal and guess who surprised his Mama and Daddy by answering two open-ended questions that were on his preschool homework assignment?
Jack! Yes, Jack!
M: Hey Jack, what is your favorite store?
M: Why is Publix your favorite?
J: Drive cart.
I love love love love love love how much he's communicating these days. If you don't understand his spoken language he will use signs, other spoken words, body language or he'll try to show you some other way what he is trying to say. Good times...
Don't forget to check out this week's Life is Therapy.