I am not 100% sure, but I think they represent the recent average speed of Waze users on that particular road. I recently wondered this myself & found only one reference to it on the web. The numbers are tiny on my (android) phone, so whatever they mean they are pretty useless (for me). What's puzzling is that they don't appear on every road.
between my autocorrect am I misspelling you sometimes need a translator to understand me. My apologies
it should say you were seeing the speed of the Waze and Google map users in front of you going through that section that is red. I suggest you swipe up from the bottom and look at routes to see if going around the traffic will save you time and keep you moving or if it's best to sit through it.
I have seen 2 beta versions where they're going to actually show you on the map alternate routes but they're not ready for public release.