Flow is just your flow of breath or inhale and exhale respirations (air movement). If you zoom way in you can actually see the individual breathes.
Like this example of mine . The breathing to the left and right of those events is normal respiration.
What you see without being zoomed in on your report are all these little respirations stacked together really close.
This image was with SleepyHead but ResScan will do the same thing.
Flow limitations are reduction in flow (air movement during breathing) that do not meet the criteria for an apnea or hyponea.
I may have to RISE but I refuse to SHINE.