adj. Used in an exaggeration of its normal meaning, to imply a total lack of comprehensibility. "The reason for that last crash is obscure." "FIND's command syntax is obscure." MODERATELY OBSCURE implies that it could be figured out but probably isn't worth the trouble.
n. Abbreviation for "open (or left) parenthesis", used when necessary to eliminate oral ambiguity. To read aloud the LISP form (DEFUN FOO (X) (PLUS X 1)) one might say: "Open def-fun foo, open eks close, open, plus ekx one, close close." See CLOSE.