The jawf is the open space inside the mouth and throat in which a long-vowel sound resonates without a precise contact point. The three letters ا، و، ي use this region when functioning as letters of madd.
Long alif: a silent alif after fatḥah, as in قَالَ.
Long waw: a silent waw after ḍammah, as in يَقُولُ.
Long ya: a silent ya after kasrah, as in قِيلَ.
Each extends its corresponding vowel sound. Artificial blocking in the throat or mouth interferes with the natural sustained sound.