# What does the word rectiplanar mean?

I have seen uses of the word 'rectiplanar' in some older math books but Google-ing doesn't really give an answer to its meaning. I have found though the following patent application where this word is mentioned and defined, but I am struggling to understand exactly what that means. The excerpt from the application is this:

In figs 1-10, the panel filter element 38 is rectiplanar, i.e. lies in a single two-dimensional plane which is rectilinear in each of such two dimensions.

Figure : fig 3 from the patent application which shows element 38

The link I have provided has these figures as well. This definition mentions that the element lies in a two-dimensional plane, but most of these pictures are 3-d. On figures 4 and 5 the panel filter element 38 looks to me like a 3-d object, so how can it lie in a 2-dimensional plane? Can anyone help me understand this definition?

• I am uncertain but I believe rectiplanar, comes from rectangular and planar, which means planes which are perpendicular to each other. Sep 26, 2021 at 13:40
• Take the word in the figure for it, it is a plane formed by two linear axes. A filter is a 3D element with uniform thickness, thus can be seen as a 2D element with thickness.
– r13
Sep 26, 2021 at 14:58
• @r13 what do you mean a 2d element with thickness? Sep 26, 2021 at 15:54
• @MichaelMunta A filter can be considered as a planar element bounded by lines with the third dimension (thickness) is uniform throughout. If the thickness varies, then it must be described as a 3D element though.
– r13
Sep 26, 2021 at 16:17
• @r13 still not really sure what you mean. Can you provide an example of an object that couldn't be represented in 2d space? Sep 26, 2021 at 16:58