Driving under the influence (DUI) refers to operating a vehicle while impaired by alcohol or drugs. This impairment can affect a person's ability to make sound judgments, react quickly, and maintain control of the vehicle, increasing the risk of accidents. Laws regarding DUI vary by location, but generally, a blood alcohol concentration (BAC) of 0.08% or higher is considered illegal for drivers over the age of 21. Penalties for a DUI conviction can include fines, license suspension, and even jail time, depending on the severity of the offense and whether it is a repeat occurrence.