Welcome to the forum Steven. I think it's commonly referred to as a light-leak. It is the digital equivalent of exposing the film to a source of light.
The simple way would be to create a blank layer fill with black and for the image above fill with a red gradient and set the blend mode of the layer to screen.
I suppose as with all things Photoshop there are a hundred ways to skin a cat, here's one for starters
but now that you have the term, you could probably find a better one or one that suits.