Factual error: Detective Nina Cassady (who was introduced towards the end of Season 17) frequently wears casual tops that show far too much cleavage for a police officer on duty. If she showed up for duty dressed like that she would be sent home to change.
Factual error: When the cops need to arrest a medical professional, they are frequently shown barging into his/her office, exam room, or even operating room. This would never happen in real life and is strictly forbidden, as it is a gross violation of the patient's privacy, and in the case of the OR, could contaminate the sterile environment, thereby jeopardizing patient safety as well.
Answer: A courtroom trial that has been terminated prior to its normal conclusion. A mistrial has no legal effect and is considered an invalid or nugatory trial. This often happens when there is a lack of Jurisdiction, an incorrect jury selection or, as seen in many of the episodes, a hung jury, i.e. some jury members finding the defendant guilty while the other members of the jury will find the defendant not guilty and all jury members won't change their decision.