PCL stands for Printer Command Language. The language is the native language of many HP printers. Some basic PCL documentation can be found at http://www.hp.com/cposupport/printers/support_doc/bpl02705.html

Windows printer drivers that talk to HP printers will almost always use PCL, unless the printer supports postscript, which is rarely the case for personal or home printers. In the UNIX world, where printers are practically expected to speak postscript, you need to set up a filter to convert the postscript into PCL. Ghostscript is usually the program used to do the actual conversion.