Perlscript is a scripting language similar to javascript or vbscript. It's developed and maintained by activestate.
It can be run on the client browser, or the server. Running it on the client requires it to have perl installed, limiting its usefulness somewhat.
Here is its faq.
I assume that a reason one might run Perlscript on a server would be if an Internet Information Server had Microsoft's Scripting Engine installed. Then one could use Perl instead of VBScript in Active Server Pages.
That approach would enable one to embed server-side Perl in HTML pages without installing Embperl.