The Wikipedia has the following information about this codepoint:
Ɗ (minuscule: ɗ) is a letter of the Latin alphabet. The lower case, ɗ represents a voiced dental implosive or a voiced alveolar implosive in the International Phonetic Alphabet. It is used with the same value in the orthographies of various languages, notably some African languages, such as Fula and Hausa, also in Sindhi and used in Shona from 1931 to 1955.
The upper case Ɗ is formed from D with the addition of a hook, or as in Shona is a larger form of the lower case letter.
In Unicode, the upper case is in the Latin Extended B range (U+018A), and the lower case is in the IPA range (U+0257).