Unique submissions

The form Limits are features which control when the form is active or inactive. The "Unique submissions" is one of the limits a form owner can use on his form.and it it makes the form limited to only one submission per user. In other words, if a form filler submits the form he cannot fill it in and submit it again, because it becomes inactive for him. This feature is used in contests, exams or polls, where an applicant cannot submit more than one entry,

Read more on how to limit your form to one user