U+0636 Arabic Letter Dad

The Wikipedia has the following information about this codepoint:

Ḍād (ﺽ), is one of the six letters the Arabic alphabet added to the twenty-two inherited from the Phoenician alphabet (the others being ṯāʾ, ḫāʾ, ḏāl, ẓāʾ, ġayn). In name and shape, it is a variant of ṣād . Its numerical value is 800 (see Abjad numerals).

In Modern Standard Arabic and many dialects, it represents an "emphatic" /d/, and it might be pronounced as a pharyngealized voiced alveolar stop [dˤ] , pharyngealized voiced dental stop [d̪ˤ] or velarized voiced dental stop [d̪ˠ]. The sound it represented at the time of the introduction of the Arabic alphabet is somewhat uncertain, likely a pharyngealized voiced alveolar lateral fricative [ɮˤ]  or a similar affricated sound [d͡ɮˤ] or [dˡˤ]. One of the important aspects in some Tihama dialects is the preservation of the emphatic lateral fricative sound [ɮˤ], this sound is likely to be very similar to the original realization of ḍād, but this sound ([ɮˤ]) and [ðˤ] are used as two allophones for the two sounds ḍād ض and ḏạ̄ʾ ظ.