A survey response is one respondent's submission for a survey, no matter whether they completed the survey or only partially answered the questions.
We collect and give you access to both completed and partial submissions in analysis, as you can find both very valuable.
Please note that we count all the responses towards the survey limit. For example, if you have a Welcome message at the beginning of the survey, each response to this will be counted. Also, if you test your survey live, those responses are counted as well.