The phrase "negative space" doesn't mean what you might think. If you're painting an apple, and someone talks about the apple's negative space, it does not actually mean that the apple's emotional state is dire. In art, negative space refers to the space around the apple.
People, animals, objects – all occupy space. We have form, shape, and weight. When you put images of us into two dimensions, we are positive space. So the apple is positive space – or a positive shape. The space around it is negative space (or negative shape).
Another word for positive space is "figure." The apple, in a painting of it, is the figure.
The negative space – the space around the apple – is also called the ground. If it's the ground in front, it's the foreground; if it's the ground in back, it's the background. Makes sense, right?
But the word background implies it's not important. It also implies that you paint it first, and then slap that apple right on top of it. If you do that, you'll have a painting of an apple slapped on top of a background. Bor-ing....
The thing to remember is that the positive and negative space are equally important in making the composition work. The negative shapes need to be interesting – not an afterthought. It's kind of like music – the notes wouldn't work without the silences between them.