Itbaq denotes close contact or enclosure involving the tongue and the upper palate, producing a distinctly enclosed and full resonance. It is more specific than istiʿla: every itbaq letter is an istiʿla letter, but not every istiʿla letter has itbaq.
Its four letters are ص، ض، ط، ظ. The letters خ، غ، ق exhibit elevation but are not members of the itbaq group.
Contrast: compare ص with س, and ط with ت. The emphatic member has a different tongue configuration and resonance. Greater vocal volume alone cannot create itbaq.