Please define in layman's terms what exactly is "gain." What are its uses?

I come across the term often, but everyone seems to have a different understanding of it. I recently read that gain is the video equivalent to ISO, however, video cameras have ISO settings as well.

Many thanks!

Depends...

Gain on a display, or gain on a camera.

On a display it is 'contrast', lifting the highlights further away from black, without affecting black.

On a camera is is a way of electronically boosting the signal. Not the same as ISO.

Steve