What are "Crisis Actors"?

"Crisis actors are supposedly professional actors used by government agencies and/or the mainstream media to deceive the public with portrayals of trauma and suffering."
https://rationalwiki.org/wiki/Crisis_actor

"A crisis actor (aka actor-patient or actor victim) is a trained actor, role player, volunteer, or other person engaged to portray a disaster victim during emergency drills to train first responders such as police, firefighters or EMS personnel."
https://en.wikipedia.org/wiki/Crisis_actor

"The first thing to understand is that the “crisis actor” conspiracy theory has a slender tie to reality. Crisis actors do exist, though there is nothing underhanded about them: they are simply performers hired to play disaster victims in emergency drills or wounded combatants in military exercises. They provide a degree of realism for people practicing for real emergencies further down the line."
https://www.theguardian.com/us-news/2018/feb/21/crisis-actors-deep-state-false-flag-the-rise-of-conspiracy-theory-code-words