Anytime a DUI arrest issue arises, the term blood alcohol concentration (BAC) comes up. This term is often heard but seldom understood. If you or a loved one has been arrested and accused of driving under the influence (DUI), you may need to have a better idea of what this term means. Read on to learn more. What is Meant by Blood Alcohol Concentration? There is a bit of confusion about this term and it is frequently confused or used interchangeably with breathalyzer results.