What do these mean: “Subject?”, “Is Open?”, “Responds to Self?”, “Self Response PID”?

"Subject?" asks whether the person has been chosen as a Subject.

"Is Open?" asks whether the Questionnaire for that person is active i.e. available for responses. If not, the questionnaire has been closed for responses, probably by generating a Report. (Questionnaires show as Open even before the "Starting Date For Responses" set on the Project tab.)

"Self-Responds?", asks whether the Subject will be invited to respond to her/his own questionnaire. To respond is the default, indicated by a checkmark. If no checkmark, the person cannot respond to their self-assessment questionnaire.

"Self Response PID" is the PID used by the Subject to respond to her/his own questionnaire.