Positive space is any part of the photo that jumps out from its surroundings. That includes your subject, for example, along with other noteworthy areas of detail. Negative space is just the opposite — parts of an image that don’t attract as much attention, surrounding the positive space. Emphasizing negative space in photography refers to using the open space in an image to draw focus to the subject – your eyes pretty much can’t help but be drawn from the nothingness to the subject. This can be achieved in a variety of ways from having a large expanse of a plain background, such as blue sky or snow, in a composition to blurring the background to your subject. Highlighting a negative space approach can sometimes mean breaking other more conventional composition guidelines by, for example, placing the subject very close to the edge of the frame or making the subject of the image relatively small.
Negative space in photography: the essential guide by Sandra Roussy
6 Ways to use negative space to create more powerful photos with your camera by Rob Pearson-Wright