A redout occurs when the body experiences a negative g-force sufficient to cause a blood flow from the lower parts of the body to the head. It is the inverse effect of a greyout or brownout

Brownout (medical)

A greyout is a transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied a loss of peripheral vision...

, where blood flows away from the head to the lower parts of the body. Redouts are potentially dangerous and can cause retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

l damage and hemorrhagic stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

.

In popular culture

The redout effect is often used in video games if the player takes damage. Apart from the visual effect, it has very little to do with medical redouts.