"Alcohol Use Disorder" is the term used in the DSM-5 to refer to physical and mental problems that are related to the use of alcohol. The DSM-5 was published in 2013, replacing the DSM-IV, in use since 1994. The earlier DSM had two different disorders for alcohol use: Alcohol Abuse and Alcohol Dependence, which were combined for the DSM-5.
In the Big Book of Alcoholics Anonymous, it is written that alcoholism is a "cunning, baffling and powerful" illness. While this is most immediately true for someone suffering from the effects of alcohol, alcohol use is also baffling for those who seek to diagnose and treat it. That alcohol has a number of negative physical and mental effects is obvious, but the exact pattern of the effects is not always easy to see. Alcoholics Anonymous itself states that there is no "objective" criterion for alcoholism, that alcoholism is the subjective feeling of powerlessness over alcohol. But from a medical and psychiatric viewpoint, there are objective criteria that can used to diagnose whether someone has a alcohol related problem.
In the DSM-IV, these were divided into syndromes of alcohol abuse and alcohol dependence. To take two extreme examples, someone could use alcohol once a month but do it in a very risky way (driving while intoxicated, starting physical fights, etcetera). This person would be an alcohol abuser, but not alcohol dependent. Or someone could use alcohol daily in a way that didn't result in antisocial behavior, but still led to physical and psychological dependence. This person would be alcohol dependent, but not an alcohol abuser. However, most medical professionals, and for that matter most laypeople who have had experience with alcohol users, know that alcohol dependence and alcohol abuse are different sides of the same coin. Although some patients might show more symptoms of either abuse or dependence, it is clinically impossible to separate them into two distinct disorders. Thus, the combined diagnosis of "Alcohol Use Disorder".
The DSM-5 uses 11 different criteria to assess whether someone suffers from an Alcohol Use Disorder. These criteria cover symptoms of both abuse ("Recurrent alcohol use in situations where it is physically hazardous") and addiction ("Craving, or a strong desire or urge to use alcohol"). A patient's level of Alcohol Use Disorder, whether it is mild, moderate or severe, depends on the number of symptoms they display.
There are many possible questions about the objectivity of the American Psychiatric Association (the authors of the DSM series), and of whether they are attuned to the entire psychosocial matrix of why people abuse alcohol. I believe that as more medical and neurological research is done, medical professionals will discover that there are several different causes, and outcomes, of alcohol use. However, I think that in general, the current DSM-5 diagnosis, which defines all symptoms of alcohol use and dependence as parts of one syndrome, is the most useful model for looking at alcohol use and abuse.