Final answer:
The term that best describes the event where an arm board falls off during surgery but is replaced before any harm occurs is a 'Near miss'. This describes a potential but averted harm in a medical setting.
Step-by-step explanation:
The term that best describes a patient safety event where an arm board falls off during surgery but is quickly replaced before the patient suffers any harm is C) Near miss. A near miss is an unplanned event that does not result in injury, illness, or damage but had the potential to do so.
In contrast, an adverse event refers to harm caused to a patient due to medical care. A sentinel event is a specific type of adverse event that results in death, permanent harm, or severe temporary harm and intervention required to sustain life. Lastly, close call is another term generally synonymous with near miss, indicating a situation where an error was averted just in time.