system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is "space - time"?
gpt
Imagine the universe is a table with ants crawling across it.  Then you could take a bunch of pictures of that table and stack them on top of each other.  The table itself is two-dimensional (flat), but the stack of photos is three-dimensional.  That third dimension is proportional to time (scaled by the rate you take photos and the thickness of each photo).  So what we have is a single object made up of two spatial dimensions and one time dimension.

Now, the real universe has three spatial dimensions.  If we were to similarly "stack" snapshots of the universe, we would get a four dimensional object, where the fourth dimension is proportional to time (scaled by the speed of light).  That's what we call space-time.