The "Avoid, Deny, Defend, Aid" terminology has been adopted by the Utah State Board of Education, as well as universities, businesses, and schools across the nation. The terminology was developed by Texas State University as a complement to their Advanced Law Enforcement Rapid Response Training (ALERRT).™
"Avoid, Deny, Defend, Aid" is similar to other response models (such as "Run, Hide, Fight") but includes important distinctions.
AVOID emphasizes that your first priority is to avoid the threat. While the best response is often to run, there may be situations where you need to move quietly to avoid detection or to assess the situation as it evolves. AVOID also acknowledges that some individuals may be physically unable to run.
DENY access to your location (such as locking and barricading doors) is a more active strategy than hiding (which implies passively concealing yourself or acting lifeless when an attacker enters the room).
DEFEND remains a "last resort" measure, but it's also your right and reinforces a survival mindset. Additionally, most K-12 schools and workplaces have zero-tolerance policies for "fighting" which may cause confusion for students/employees as they consider how to respond.
AID focuses on providing life-saving assistance to others when it is safe to do so, such as controlling bleeding until first responders arrive.
Regardless of which terminology you choose, the most important thing is to have a plan and remember that you have options for how to respond in an active threat situation.