A response is an answer submitted using a form or survey on the Collect App. One response refers to one complete survey submission.
A response is an answer submitted on a survey form using the Collect app. Each response which is submitted after answering all the questions on one form on the Collect mobile app (irrespective of the number of individual questions in the form) constitutes a form response.
Let's take an example where you have 1 form on which data will be collected by 10 users/mobile devices. If each user fills all the questions on your form and presses the "Submit" button on the app once, you would have collected 10 responses.