Also Lisp-related: `sexp' is an abbreviation for `s-expr', itself an abbreviation for `s-expression', itself an abbreviation for `symbolic expression'. A sexp is simply a Lisp expression (be it code or data); `s' distinguishes it from the `meta-expressions' of early Lisps (McCarthy's 1.5, for example). In these Lisps, programs could be expressed with an Algol-derived syntax (m-exprs), or with the parenthesised notation that was also used for expressing lists (s-exprs). s-exprs caught on; m-exprs didn't. Now, almost forty years later, you'll be hard-pressed to find someone who knows what an m-expr is. Then again, you would have back then, too.