In a questionnaire, questions where the possible answers are not predetermined and thus allow for personal, qualitative answers. Such answers cannot be automatically marked but require judgement.
Questions in which no options for response are given, as many responses are possible. These types of questions are used to facilitate new ideas for an organization. Ex. Who is your favorite politician
A question is open if it invites elaboration. An open question will set no parameters (or very minimal parameters) for the answer. They are questions that cannot be answered with a "yes" or "no" response.