PostScript is called the page description language; it is a programming language developed by Adobe to define data for printing. As a familiar example, the internal structure of a PDF is based on PostScript.

As a lot of the outline information of OpenType fonts is described in PostScript, it is a necessary format in font engineering.

To give a bit more detail, PostScript originally had specifications related to font, which were inherited (integrated with specifications for TrueType) to create specifications for OpenType font as a background.

As an example, saving the following code with the “.ps” extension and opening with Adobe Illustrator, etc. allows you to check the rendering content.

%!
%%BoundingBox: 0 0 595 842
newpath
100 100 moveto
100 200 lineto
200 200 lineto
200 100 lineto
closepath
stroke
showpage

If you would like more detailed specifications, please refer to the document below:
https://www.adobe.com/jp/print/postscript/pdfs/PLRM.pdf
(Path Construction Operators on page 518)

(LN)