What does the risk rating (Low, Medium, High) actually mean?

Low Risk means no significant obstacles were found and your mark is likely registrable — you can proceed with confidence. Medium Risk means there are potential concerns (such as similar marks in related classes or possible examiner objections) that may require strategy adjustments, but registration is still achievable. High Risk means significant conflicts or registrability issues were identified, and you may need to modify the mark, narrow the goods/services scope, or consider an alternative approach before filing.