This is where your DUI attorney, after reviewing all the evidence (police reports, blood/breath test etc.) and fully investigating your case (interviewing officers/witnesses etc.) comes to an agreement with the State/City Prosecutor on amending or reducing your DUI charges. Most often, this happens at the DUI pre-trial hearing, but can happen any time in the proceedings, even right before the jury trial itself.
The plea bargain (or dismissal) may also be obtained by the suppression of critical evidence at pre-trial motions. Examples of typical plea bargains in DUI cases are Reckless Driving, Reckless Endangerment and Negligent Driving among others. (what's acceptable depends on the evidence and your personal situation) Therefore, it is important your DUI attorney is aggressive in contesting all the evidence against you and he/she gets the best resolution for you.