The full definition of a Universe is as follows: a list of locations referencing a single framing geometry.
This needs to be understood in context. The context is called "3D", and it describes a tool, quite familiar in our contemporary world, which is constructed as follows: a list of locations is place into the memory of a computer, together with a program which generates imagery on a screen based on the contents of the list and a certain user input.
The program, running on the computer, accepts user inputs. One of those inputs is the list of locations. The other is a specific location which describes a camera.
Let us say that our location list includes a cube, which is a location, whose specifics are listed. That's the list input, and then an abstract but representative version of the camera input specifies that the camera is in a certain location pointing at the cube. There will then appear, on the screen, an image of the cube.
This is what the 3D tool does.
