In short...
A response is counted if a participant completes your survey once, regardless of how many questions or question groups your survey contains.
In a more detailed description...
- A survey is taken and completed => 1 response
- A survey is taken and only partially completed => 0.5 response
- A response is manually entered by an administrator => 1 response
- A partially completed survey is marked as finished by an administrator => 0.5 response