Road munching, is the points you get for driving on roads that have the dots, and turn into a Waze Pacman ®.
Road munching is when you drive on a segment which was newly added to the map, and is working properly. No GPS track has validated them yet. Not that they haven't been driven, but that the GPS tracks resemble the road close enough to validate, or enough modifications have been done, that Waze wants to encourage someone to drive it again.
The goal is road validation.