It's called space-time. All it means is that we need 4 coordinates to locate anything. In fact, you do this intuitively. For example, Sue's head is 4 feet from the door, 3 feet from the wall and 5 feet above the floor. Can Joe occupy the same location? Sure he can, as long as he does it at a time when Sue isn't there! This is space-time. We know this intuitively, so the idea of space-time is really just common sense, but now we have a name for it.

Einstein's genius, like Newton's, was to strip away assumptions about the world around us to look at nature with new, clearer eyes. Einstein suspended his assumptions about space and time itself. When he did so, he realized that not only are space and time connected, but mass itself is woven intricately into space-time. That is, we don't occupy space as time flows by, but rather, the matter of our beings is part of space-time itself. Mass seizes space and time like a blanket and wraps itself up in it. The mass of your body changes the shape of space-time around it. And the more massive or compact the body, the more the shape of space-time is pushed, stretched and wrinkled. This is the essence of Einstein's theory of General Relativity.