metasyntactic variable

n. A name used in examples and understood to stand for whatever thing is
under discussion, or any random member of a class of things under
discussion. The word foo is the canonical example. To avoid confusion,
hackers never (well, hardly ever) use foo or other words like it as
permanent names for anything. In filenames, a common convention is that any
filename beginning with a metasyntactic-variable name is a scratch file that
may be deleted at any time. Metasyntactic variables are so called because
(1) they are variables in the metalanguage used to talk about programs etc;
(2) they are variables whose values are often variables (as in usages like
the value of f(foo,bar) is the sum of foo and bar ). However, it has been
plausibly suggested that the real reason for the term metasyntactic variable
is that it sounds good. To some extent, the list of one's preferred
metasyntactic variables is a cultural signature. They occur both in series
(used for related groups of variables or objects) and as singletons. Here
are a few common signatures: foo , bar , baz , quux ,  quuux, quuuux...:
MIT/Stanford usage, now found everywhere (thanks largely to  early versions
of this lexicon!). At MIT (but not at Stanford), baz dropped out of use for
a while in the  1970s and '80s. A common recent mutation of this sequence
inserts qux before quux. bazola, ztesch: Stanford (from mid-'70s on). foo ,
bar , thud, grunt: This series was popular at CMU. Other CMU-associated
variables  include gorp. foo , bar , bletch: Waterloo University. We are
informed that the CS club at  Waterloo formerly had a sign on its door
reading Ye Olde Foo Bar and Grill ; this led to an attempt  to establish
grill as the third metasyntactic variable,  but it never caught on. foo ,
bar , fum: This series is reported to be common at XEROX PARC.