Direct Printing is printing direct to the port, formerly known as "pass-through" printing. Printer language and control vary for each printer, so for this reason this legacy method of printing has mostly been replaced with Native Windows Printing.
Printing directly to a network, indicated by NAME=PRN:/ can set a printer as the direct port printer, instead of the original PRN:/10
Also, another printer initialization keyword is supported for direct printing:
PRINTER xxx INIT HP "..."
This adds certain required keywords to the printer initialization sequence. Some laser printers require these settings for Direct printing. They were previously provided automatically by pass-through printing (the predecessor to Direct printing).
The Printing article contains information about this and other printing processes.