Reflex/ˈriːfleks/ Definition 1 of 4Pro Tip 1/3Involuntary Action Reflex refers to actions your body does automatically, without you deciding to do them. Knee-jerk is a common reflex test by doctors. Pro Tip 2/3Not Deliberate A reflex isn't controlled by conscious thought; it happens instinctively. Blinking when something approaches your eyes is a reflex. Pro Tip 3/3Quick Response Reflex actions are typically very fast, protecting us from harm. The reflex to cough instantly clears the throat.