metacharacter
/ˈmɛtəˌkarɪktə/noun
1 Philosophy. The character of a concept, etc., in a metalanguage; metalinguistic character. rare.
2 Computing. A character that is defined as having a controlling role by the computer program or operating system in use, and that gives information about how other characters are to be determined or gives rise to a specific action.
Origin
1960s; earliest use found in Mind. From meta- + character.