This character is a Other Letter and is mainly used in the Arabic script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written as Arabic letter from right to left. When changing direction it is not mirrored. The word that U+0630 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 6 other glyphs.
The Wikipedia has the following information about this codepoint:
Ḏāl (ذ, also be transcribed as dhāl) is one of the six letters the Arabic alphabet added to the twenty-two inherited from the Phoenician alphabet (the others being ṯāʾ, ḫāʾ, ḍād, ẓāʾ, ġayn). In Modern Standard Arabic it represents /ð/. In name and shape, it is a variant of dāl (د). Its numerical value is 700 (see abjad numerals). The Arabic letter ذ is named ذَالْḏāl. It is written in several ways depending in its position in the word:
The South Arabian alphabet retained a symbol for ḏ, .
When representing this sound in transliteration of Arabic into Hebrew, it is written as ד׳.
This sound is found in English, as in the words "those" or "then". In English the sound is normally rendered "dh" when transliterated from foreign languages, but when it occurs in English words it is one of the pronunciations occurring for the letters "th".