PSTricks is a set of macros that allow the inclusion of PostScript code (e.g. drawings) directly inside (La)TeX code. It is originally the work of Timothy Van Zandt and in recent years it has been maintained by Denis Girou, Sebastian Rahtz and Herbert Voß.
Note that documents that use PSTricks need to be compiled either with
XeLaTeX. If you want to compile with
pdflatex then see How to use PSTricks in pdfLaTeX?