Alwood is right.
Euclid laid out the theorems for Plane Geometry. All objects in this study exist in a single plane, and also exist only in theory!
They have only two dimensions, (x,y) aka length and width...but have no third dimension (z) aka depth or thickness, and therefore can't be physically "picked up"...only "slid" around in one plane
, and hence are only theoretical, (but very useful) mathematical tools.
A short book (written decades ago), fairly easy read if anyone on this forum wants to enrich themselves with an interesting perspective (no pun intended) within a world based in only one plane and the short story of it's dwellers, and how they must move about.
The title of the novella is "Flatland", forgot the author, but can be found online used @ B & N, Amazon, etc.
Google (flatland), the book, not the Brooklyn neighborhood!
Hey forum, please don't send out the "guys in the white coats" to pick me up, as I already fear I'm on their RADAR