Which file on a BSD system defines the printers which are available by the Ipr...

The /etc/printcap file on a BSD system defines the printers that are available by the Ipr printing system. The Ipr printing system is a BSD-compatible printing system that uses the lpd daemon to manage print jobs and spooling. The /etc/printcap file contains a series of entries, one for each printer, that specify the printer name, device, options, and filters. The format and syntax of the /etc/printcap file are described in the printcap(5) manual page. References:

About Printing on FreeBSD | The FreeBSD Forums

The BSD Printing Protocol (System Administration Guide, Volume 2) - Oracle

Chapter 11. Printing | FreeBSD Documentation Portal