Definition of "maddah"

Arabic diacritic similar in appearance to a tilde. Over an alif (آ (ʔā) "alif maddah"), it indicates glottal stop, /ʔ/, followed by a long /aː/. The diacritic is not used separately, only over alif. Alif maddah can appear in the beginning: آسِف (ʔāsif) or in the middle of a word: قُرْآن (qurʔān).  examples

In the Qur'an, it indicates an extra long vowel and can appear over any long vowel.  examples

In Persian the letter is used only in the beginning of a word with a long /aː/: آمدن (âmadan).  examples