A "JAPH" is a snippet of code that, when executed, prints out (in some form) "Just Another Perl Hacker". To my understanding, one of the requirements is generally that those words not appear in the code. The snippets were (if memory serves) popularized by merlyn, who wrote quite a number of them.

Hope that helps. (And anyone who notes any errors in what I said, please let me know or reply. Thanks in advance.)