In my first sales training class I discovered open and closed questions and the purposes they can be put to. Subsequently this was refined to open, probing and closed questions and their purposes, rapport building, discovery, clarifying and confirming...
Open questions allow the person you are asking to answer in their own words. They start with "what" or "how". e.g "How are you?"
A subset of open quesitons are probing questions: These are still open but are more focused on an area you are interested in. They also start with "what" or "how" but equally can begin with "tell me about" or "help me understand" e.g. help me understand how you are dealing with X"
e.g. What plans do you have for the holidays?
Closed questions are those that have yes, no, a limited number of responses (e.g. "do you like a, b or c?) or a number (how old are you? What shoe size are you?)
You use closed questions to clarify or confirm your understanding e.g. "so you're going to Bali for the holidays?" and, "you prefer beach holidays correct?"
Ask too many open questions and the conversation can ramble and be unfocused, too many closed questions and the answerer can feel like the being interrogated