Definitions for "Metacharacter"
character or (shift-) key to be interpreted as modifying the value of the character (or key) following it in a string (or produced simultaneously in typing), either by prefixing a special character (" ^X-Q terminates the program"), or by interpreting it literally, thus escaping the default special interpretation of the following character.
a single character that is used in place of another character or set of characters.
In a regular expressions, a metacharacter is a special character that is expanded to match patterns.
Keywords:  tells, request, sign, search, typed
a typed sign that tells the search how to process the search request