Wiktionary
n. (context art English) The space around and between the subject(s) of an image.
Wikipedia
Negative space, in art, is the space around and between the subject(s) of an image. Negative space may be most evident when the space around a subject, not the subject itself, forms an interesting or artistically relevant shape, and such space occasionally is used to artistic effect as the "real" subject of an image.
Usage examples of "negative space".
How does the Vanderguerre theory of negative space explain that one?
The arch was just visible, a chord of negative space cutting into the Milky Way just above the horizon.
This null-space cluster contracts further, and then -- speaking figuratively -- the whole turns inside out, into the realm of forbidden energy states, into 'negative space,' so that it is not nothingness, but less than nothingness -- mathematically, at least!
The negative space between construction-sites defined new streets now, only a little wider and straighter than the old.