olemus
ISO/IEC 2382: kirjamärk,
- mis pole täht, number ega tühimärk ja
- mis tavaliselt pole ideogramm

näiteid
http://reference.wolfram.com/language/guide/SpecialCharacters.html

https://www.wired.com/2010/02/special_characters/

https://www.yourhtmlsource.com/text/specialcharacters.html

paroolides
https://www.owasp.org/index.php/Password_special_characters

https://docs.oracle.com/cd/E11223_01/doc.910/e11197/app_special_char.htm#MCMAD416