Standard questions are custom questions that a company's Lyyti users can create, and they will then be available in all the company's events. The important point for API developers is that these questions will always retain the same ID in all events, so the type of a participant's answer can be identified.
A common use case is to have a standard question for an internal ID used to identify people in the company's intranet. The intranet can then add a participant using the API's participants POST resource AND add an answer to this question, and then redirect the user to their personal participation link. The internal ID will already be filled. Other fields such as email and name can also be pre-filled in this way, so the user doesn't have to fill them themselves, and the risk of typos will be minimized.
Note that in order for these standard questions and their answers to be available, they have to be enabled in Lyyti by the user managing the event.