A question is a type of sentence that needs an answer.
What time is it?
Where are you?
Why are you crying?
When can I go out to play?
Who is that man?
How much does that cost?
Did you notice that nearly all these questions start with words beginning with 'wh'? They are sometimes called question words or 'wh' words.
We have to remember that 'how' is the odd one out, but it is still a question word.