To my understanding, the broad definition of a closed question is that it can be answered in one word, one phrase, or one short sentence. For example, the closed question "Did you see this movie?" can be answered in one word (Yes), in one phrase (Yes, I did), or in one short sentence (Yes, I saw it yesterday). However, there is also a narrow definition of a closed question, which requires it to be answered by YES or NO only. This can be achieved by drop-down menus in questionnaires.
On the other hand, open questions deliberately invite to give a longer answer and are good conversation starters. So, instead of asking "Did you see the movie?", one could ask "How did you like the movie?". Open questions can be asked by using question words such as why, who, how, etc.
While closed questions, require the respondent to simply react, open questions require them to think, reflect, and reveal their opinions, emotions, and details.
