Each survey is classified as either Anonymous or Non-anonymous. You can choose this option while creating the survey.
An anonymous survey is used to get feedback from the users allowing them to give prompt feedback anonymously. No user identifiable data will be recorded for the responses they will provide including usernames, ip addresses etc.
A non-anonymous survey is something which allow you as a survey administrator to know who is giving feedback and what feedback he/she is giving. In this survey type username(if user is logged in), ip address, country details are recorded.
Please note that an INFORMATION DISCLOSURE notice is displayed that will let the respondents know about the survey type before they respond to the survey.