The traction grade rates the ability of your tyre to stop on wet pavement.  Traction performance is given as AA, A, B or C, which you will find on the sidewall of your tire.  Tires with an AA grade stop faster on wet pavement than those with a B or C grade.  So AA is the highest rated while C is the lowest rates.  The traction tests do not test tyres for cornering, acceleration, driving at high speed or driving on dry roads and cover straight line braking only.