A penis, as defined in leet or 1337 speak. In the early 90s when people started using keyboards, they decided everything looks cooler if you can replace letters with numbers or add z's and r's to words. Similar words are Haxor, lulz, warez ect.
This still happens in 2012, however it has become an ethnic thing mostly because they cant spell. not because they think its funny like we did in the 90's.
90's usage: The Warez MIRC chatroom waz lame so I smurfed all the penorz! Im so uber 1337!! ROFLCOPTER!!
Modern day: That bitch was crazy so I had to whip out my penorz and smack her in the face with it.
2012 ethnic usage: Yun, DaT shiZ was DA PenorZ. LiL WaYn3 For3vRZ!