HD traffic stands for High Definition traffic
It is a service that has been put into the market by TomTom (the full service is TomTom HD-Traffic as well). TomTom HD Traffic offers traffic information on the entire major road network in the Netherlands, including all secondary "N" roads. The supplied cover is up to 10x better than with TMC, and refreshes every 3 minutes. Read more about HD-Traffic on the TomTom website. TomTom HD-Traffic