Lens flare

Light hitting the front element at an angle scatters between the glass groups instead of forming an image, and what reaches the sensor is veiling haze that lifts the blacks, or a chain of coloured ghosts running back towards the light. Cheap lenses and dirty or scratched front elements flare far more, as do filters.

A lens hood or a flag just outside the frame kills most of it, and your own hand held above the lens works in a pinch. Deliberate flare is a style, so plenty of creators add it in post, and doing it there gives you control over shape and strength that the real thing does not.