Time for another photo term definition and a return to the days of developing film.
Burning: When you made an enlargement of a photo, you had to project the negative onto a piece of light sensitive photo paper. The longer you allowed it to project on the paper, the darker it got. So if you wanted one area to be darker than another area, you would put your index finger and your thumb together to make a hole and allow more light to pass. Hence you were burning the picture. And, if you look closely at the symbol Photoshop uses for burning, it's an image of a hand making a hole with the first finger touching the thumb. Usually you used 2 hands in real life, but it's close enough.