Postscript is a programming language. It was developed by Adobe, in 1984. It is a standard used by many computer printers. There are three different versions of it, Postscript Level 1, Level 2, and Level 3.
The Portable Document Format is another standard, also from Adobe. It is better adapted to printing. Many things computer languages have, have been dropped to develop PDF.
And finally, a Hello World program, the customary way to show a small example of a complete program in a given language, might look like this in Postscript:
%!PS /Courier findfont 20 scalefont setfont 72 500 moveto (Hello world!) show showpage
or if the output device has a console
%!PS (Hello world!) =