∂

The symbol was introduced originally in 1770 by Nicolas de Condorcet, who used it for a partial differential, and adopted for the partial derivative by Adrien-Marie Legendre in 1786.^[3] It represents a specialized cursive type of the letter d, just as the integral sign originates as a specialized type of a long s (first used in print by Leibniz in 1686). Use of the symbol was discontinued by Legendre, but it was taken up again by Carl Gustav Jacob Jacobi in 1841,^[4] whose usage became widely adopted.^[5]

The symbol is variously referred to as "partial", "curly d", "funky d", "rounded d", "curved d", "dabba", "number 6 mirrored",^[6] or "Jacobi's delta",^[5] or as "del"^[7] (but this name is also used for the "nabla" symbol ∇). It may also be pronounced simply "dee",^[8] "partial dee",^[9][10] "doh",^[11][12] "dow" or "die".^[13]

The Unicode character U+2202 ∂ PARTIAL DIFFERENTIAL is accessed by HTML entities ∂ or ∂, and the equivalent LaTeX symbol (Computer Modern glyph: ${\displaystyle \partial }$ ) is accessed by \partial.

∂ is also used to denote the following:

• The Jacobian ${\displaystyle {\frac {\partial (x,y,z)}{\partial (u,v,w)}}}$ .
• The boundary of a set in topology.
• The boundary operator on a chain complex in homological algebra.
• The boundary operator of a differential graded algebra.
• The conjugate of the Dolbeault operator on complex differential forms.
• The boundary ∂(S) of a set of vertices S in a graph is the set of edges leaving S, which defines a cut.

• d'Alembert operator
• Differentiable programming
• Differential operator § Notations
• List of mathematical symbols
• Notation for differentiation
• 𝒹 (Unicode MATHEMATICAL SCRIPT SMALL D)
• ꝺ (lowercase d in Insular script)
• δ (lowercase Greek Delta)
• д (lowercase Cyrillic De, looks similar when italicized in some typefaces)