Dyslexia is a specific learning disability that primarily affects a person's ability to read, spell, write, and sometimes speak. It is not related to intelligence, and individuals with dyslexia may struggle with phonological processing (the manipulation of sounds), which affects word recognition and reading fluency.
Other options explained:
Illiteracy: Inability to read or write, but not necessarily caused by a cognitive disorder.
A person who knows more languages: That describes a polyglot, not dyslexia.
A person who can only read but unable to write: That condition doesn't define dyslexia specifically.