Hmmm well if I remember correctly from my brain injury rehab days it is a scale 3-15 each rating is related to levels of consciousness. The better the response the higher the scale rating. 15 being more like concussion ~ the lower the number the less the response. It rates response to stimuli. Some reaction is mere posturing. Pain reactions can be noticed but also reactionary. Pain then can become more reactionary or vocal increasing rating. Alertness and responding to stimuli with physical and hopefully verbal response is also monitored.
Levels 3-8 are considered in some state of coma 3 severe as the scale number improves the level of consciousness also improve to say semi-coma status.
Levels 8-15 are more alert and functional status with of course the higher the scale the more conscious and accurate reaction and response internal and external stimuli. Just my version of course :)