This message from the C shell csh(1) indicates that a user typed a command containing a backquote symbol (`) without a closing backquote. Similar messages occur from an unmatched single quote (') or an unmatched double quote ("). Other shells generally give a continuation prompt when a command line contains an unmatched quote symbol.
Correct the command line and try again. To continue typing on another line, give the C shell a backslash right before the newline.