Ghain is the final letter of the modern Arabic language and has a numeric value of 1000. In the Sufi tradition: The ‘ghain’ is the nineteenth letter of the Arab alphabet. It represents number one hundred and belongs to the element of earth, while in North Africa it is believed to belong to the element of water. It symbolizes total mystery
Cited from website Sufi glossary.

The Arabic letter غ (called غين ghain, ghayn, or ġayn), commonly known in Egypt as [ɣeːn], is one of the six letters in the Arabic alphabet not in the twenty-two akin to the Phoenician alphabet (the others being ṯāʾ, ḫāʾ, ḏāl, ḍād, ẓāʾ). It is the twenty second letter in the new Persian alphabet. It represents the sound /ɣ/) or, in the case of Classical Arabic, /ʁ/. In name and shape, it is a variant of ʻayn (ع). Its numerical value is 1000 (see Abjad numerals). http://en.wikipedia.org/wiki/Ghain