Response limits allow you to close a survey automatically after you get a certain number of responses. This is especially useful if you are using surveys for registrations that have a limited number of spots.
To set the response limit, go to the "Access Controls" for the survey and click the checkbox to limit the number of responses. Then type the number of responses you want the survey to be limited to.
Once the response limit has been reached, the survey close message you define on the Access Controls tab will show to any respondents who try to take the survey after the limit has been reached.