In this picture, i really love how the shadows are. The contrast between dark and light are really nice in this image. We one lighting for this image which is the main lighting to cast the shadows.
The Fill light fills up the shadows so we can see more of the portrait and the back light fills the background with light. And finally the main light casts shadows on our subject(s)
there is a big difference between a background light and backlight. a background light shines on the background and creates separation between the subject and the background. A backlight aims towards the camera from the opposite side of the subject. It often leaves the main subject in the dark, creating a silhouette.