What is the difference between alcoholism, and grey area heavy use?
Alcoholism involves physical dependence on alcohol that leads to compulsive drinking regardless of negative health effects, especially causing physical changes in brain structure and function. Grey area heavy use refers to frequent consumption above recommended levels but below addiction criteria. 

Both conditions impair judgment, coordination, memory and reasoning abilities due to neurotoxic effects of extended ethanol exposure. Both disrupt social functioning in the short and especially the long term dependence, both lead to structural damage in areas controlling learning & behavior regulation. 

The main difference is that alcoholism causes severe impairments, whereas grey area users tend to temporary maintain control over most areas of life except drinking which will lead to inevitable alcholism unless prevented ahead of time.
Thanks for the explanation, it helps differentiate the two. I have a follow-up question though.. How would alcohol use factor in a broader history of mental health issues and trauma? If alcohol use can be understood as a coping mechanism, albeit a very dysfunctional one, does it matter if/when grey area use become alcoholism?