This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
SCMS (Serial Copy Management System) is a copy-protection system
intended to stop rampant piracy of commercial recordings to
digital tape. SCMS allows the home taper to copy from a CD to a
digital tape, but prevents anyone from digitally copying that
new digital tape.
You CANNOT hear SCMS.