What ⅆ means
It marks the differential in some mathematical notation. In an integral, it identifies the differential attached to the integration variable, rather than acting as an ordinary variable. Many writers use an upright or math-italic d instead.
Unicode groups ⅆ with four related double-struck italic math symbols: ⅅ for the capital differential D, ⅇ for the exponential e, and ⅈ and ⅉ for the imaginary units i and j.
Why is ⅆ double-struck?
The doubled strokes distinguish a mathematical role from an ordinary letter. The style grew from practical attempts to make bold mathematical notation legible on blackboards and typewriters in the late 1950s. It spread through mathematics departments in the early 1960s and appeared in printed mathematical books by the mid-1960s.
In modern equations, the same differential may appear as ⅆ, an upright d, or a math-italic d. American and European mathematical conventions can give the same role different visual treatments.
Part of the collection
Don't confuse it with
2
Questions people ask
1Why does ⅆ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
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How to type or find ⅆ
- Search it as
- differential d · differential symbol · math d · double-struck d · blackboard bold d · mathbb d · U+2146
- Shows up in
- Anything that takes text · its shape is whatever your font draws
ⅆ\2146Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.