jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
1. [common] Not ‘Frequency Modulation’ but rather an abbreviation for ‘Fucking Manual’, the back-formation from RTFM. Used to refer to the manual itself in the RTFM. “Have you seen the Networking FM lately?”
2. Abbreviation for “Fucking Magic”, used in the sense of black magic.