A sign (ء (ʾ) - a stand-alone hamza) used in the written Arabic language representing a glottal stop. Hamza may appear as a stand-alone letter or most commonly diacritically over or under other letters, e.g. أ (ʾ) (over an alif - ا), إ (ʾ) (under an alif), ؤ (ʾ) (over a wāw - و (w)) or ئ (ʾ) (over a dotless yāʾ - ى). The exact seat of hamza is governed by an orthographic rule - "seat of hamza rule".