Shape - Any graphical 2D or 3D object created by OpenSCAD.
Design - An OpenSCAD creation (that is, an OpenSCAD program), 
which usually consists of a combination of multiple shapes.
Operation - An OpenSCAD command that changes the appearance/
properties of one or more shapes.
Parameter - Any value that specifies characteristics of shapes, operations, modules, or functions.
Preview - The process of quickly displaying a design on-screen.
Render - The process of fully evaluating the geometry of a design (and 
showing it on-screen). Once it’s rendered, you can export a design.
Units - All dimensions in OpenSCAD are specified in units. A unit 
is usually a millimeter (by 3D-printing industry convention), but 
OpenSCAD is technically unitless. All models should be explicitly sized 
in 3D-printing preparation software just prior to printing.
Width - The dimension associated with the x-axis, which is the “leftright” axis when 3D printing.
Length - The dimension associated with the y-axis, which is the 
“forward-backward” axis when 3D printing.
Height - The dimension associated with the z-axis, which is the “updown” axis when 3D printing.
2D shapes - Shapes with a width and length, but no height.
3D shapes - Shapes with a width, length, and height