Descriptions for current_location.type field for Vehicle Location?

Does anyone have descriptions of the 'type' field within the 'current_location' object of any of the versions of the "vehicle_location" API endpoints?

So far, I can see the following, but do not know what they actually mean:

breadcrumb
engine_start
engine_stop
gps_moving
gps_stopped
vehicle_moving
vehicle_stopped

I can guess most, but 'breadcrumb' makes me worry. Am I not receiving the latest location of this vehicle? I have also seen a number of 'gps_stopped' with a 'speed' greater than 0.

So - what do they all mean, and have I missed any types in the list above?