Universally recognized nickname for the book Programming Perl, by Larry Wall and Randal L. Schwartz, O'Reilly and Associates 1991, ISBN 0-937175-64-1 (second edition 1996, ISBN 1-56592-149-6; third edition 2000, 0-596-00027-8, adding as authors Tom Christiansen and Jon Orwant but dropping Randal Schwartz). The definitive reference on Perl.