Space is considered the boundless three dimensions that objects are able to move relative to.
Space is so interesting, but so complicated! Does it really go on forever?
Yes there is no end.  There is also a boundless four dimensional continuum called spacetime.
I didn't realize! Do you study space for a living?
No, but the concept of space is fundamental to understanding the physical universe.
My son is really into space. He's always talking about black holes and how neat they are. What is a black hole?
Black hole
A black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In
Space
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework.