By Google definition, a flow visualization demonstrates a route, and reveals the actual path as an user explores the possible route.

“Flow reports in Google Analytics illustrate the paths that users take through content. In a single graphic, you can see how users enter, engage, and exit your content. You can also use these reports to troubleshoot your content by finding any unexpected place users exit or loop back.” https://support.google.com/analytics/answer/2519986?hl=en

http://cutroni.com/blog/2011/10/19/path-analysis-in-google-analytics-with-flow-visualization/