Any single point on such a diagram is known as an "event". Separate events are considered to be "timelike separated" if they differ along the time axis, or "spacelike separated" if they differ along the space axis. If the object were in free fall, it would travel up the "t"-axis; if it accelerates, it moves across the x axis as well. The actual path an object takes through spacetime, as opposed to the ones it "could" take, is known as the "worldline". Another definition is that the light cone represents all possible worldlines.