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.
See foo, bar, foobar, baz?, quux?, fred?, barney?, xyzzy, thud?