open-mouthed form (statue)
Buddhist term for a statue with an open mouth, representing the first sound 'a' of 'aum' (阿吽). Often paired with 吽形 (うんぎょう), the closed-mouth form.
The Agyō of the Niō statues has its mouth open.
From the Sanskrit syllable 'a' (अ), the first sound of 'aum'. The kanji 阿 is used phonetically (ateji) for 'a', and 形 means 'form' or 'shape'.