Using a substance in such a way that it prevents you from being able to deal with other aspects of your life such as maintaining social relationships, your job, etc. etc.
I would agree with this.
Although, to be honest, the definition of abuse is vague - widely differing definitions of drug abuse are used in public health, medical and criminal justice contexts.
I would agree with D3x! as well, to an extent, that using a substance excessively (so that it interferes negatively on aspects of your life as noted above) or using a substance for its non-intended purpose might also be considered abuse.
In psychiatry, the DSM-IV-TR criteria for diagnosing substance abuse are as follows:
A. A maladaptive pattern of substance use leading to clinically significant impairment or distress, as manifested by one (or more) of the following, occurring within a 12-month period:
- Recurrent substance use resulting in a failure to fulfill major role obligations at work, school, or home (e.g., repeated absences or poor work performance related to substance use; substance-related absences, suspensions or expulsions from school; neglect of children or household)
- Recurrent substance use in situations in which it is physically hazardous (e.g., driving an automobile or operating a machine when impaired by substance use)
- Recurrent substance-related legal problems (e.g., arrests for substance-related disorderly conduct)
- Continued substance use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of the substance (e.g., arguments with spouse about consequences of intoxication, physical fights)