ذ

is one of the six letters the Arabic alphabet added to the twenty-two inherited from the Phoenician alphabet (the others being , , , , ). It represents the voiced dental fricative ( voiced dental fricative). In name and shape, it is a variant of .This sound is found in English, as in the words "those" or "then". In English the sound is normally rendered "dh" when transliterated from foreign languages, but when it occurs in English words it is one of the pronunciations occurring for the letters "th".The  South Arabian alphabet retained a symbol for , .
See more at Wikipedia.org...