Let’s use physical dimensions. [data dimensions also work].
Let’s say you have a complex 3D object. If you want to describe its surface you have to unwrap it so it lays flat and then describe it 2 dimensionaly.
Or the total of a column of numbers. If you have just the total, you’re at a higher dimension – the ‘object’ representing a lot of “other things”. But where are those other things?
They’re in the total but you can’t get to them from the total.
You have to “unwrap” the total, lay it out flat to see what made up that total.
Or a volume. You have a rectanglar shape with a particular volume. To understand the 3D volume to get more answers, such as the length and width and heght of the container, you have to go down to the area of the sides – down to 2D.