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?