The Arabic letter غ (Arabic: غين‎ ġayn/ghayn) 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 Persian language it represents [ɣ]~[ɢ]. In name and shape, it is a variant of ʿayn (ع). Its numerical value is 1000 (see Abjad numerals).

A voiced velar fricative /ɣ/ or a voiced uvular fricative /ʁ/ (usually reconstructed for Proto-Semitic) merged with Ayin in most languages except for Arabic, Ugaritic and older varieties of the Canaanite languages. Canaanite languages and Hebrew later also merged it with Ayin, and this merger was complete in Tiberian Hebrew. The South Arabian alphabet retained a symbol for ġ, .

The letter ġayn (غ) is sometimes used to represent the voiced velar plosive /ɡ/ in loan words and names in Arabic and is then often pronounced /ɡ/, not /ɣ/, such as the word for Bulgaria (بلغاريا). Other letters, such as ج‎, ق‎,‎ ك‎ (also ݣ‎, ڨ‎, گ; not standard letters), can be used to transcribe /ɡ/ in loan words and names, depending on whether the local variety of Arabic in the country has the phoneme /ɡ/, which letter represents it if it does, and on whether it is customary in the country to use that letter to transcribe /ɡ/. For instance, in Egypt, where ج is pronounced as [ɡ] in all situations, even when speaking Modern Standard Arabic (except in certain contexts, such as reciting the Qur'an), ج is used to transcribe foreign [ɡ] in virtually all contexts. In many cases غ is pronounced in loan words as expected—/ɣ/, not /ɡ/—although, the original language had /ɡ/.