Final answer:
The condition of diminished physical or mental faculties due to consuming alcohol/drugs, legally defining one's ability to drive, is known as impairment, detected through law enforcement observations and potentially measured by BAC levels.
Step-by-step explanation:
The condition of diminished physical or mental faculties as a result of consuming alcohol and/or drugs, and which is legally defined for the purposes of operating a motor vehicle, is known as impairment. Objective evidence of an accused driver's impairment mainly comes from observations made by law enforcement officers, such as performance on the Field Sobriety Test. These observations may include evidence of lack of coordination, blurred vision, and difficulties with judgment, which can result from the depressant effects of alcohol on the central nervous system. Alcohol intoxication is typically indicated by a blood alcohol concentration (BAC) that exceeds legal limits, which may be measured using devices such as a Breathalyzer.