From The Jargon File (version 4.4.7, 29 Dec 2003):
runes
pl.n.
1. Anything that requires heavy wizardry or black art to parse: core
dumps, JCL commands, APL, or code in a language you haven't a clue how to
read. Not quite as bad as line noise, but close. Compare casting the
runes, Great Runes.
2. Special display characters (for example, the high-half graphics on an
IBM PC).
3. [borderline techspeak] 16-bit characters from the Unicode multilingual
character set.