∂

∂ or $\partial$ is a mathematical symbol, derived from Greek delta, often read as "der", "del", "dow", "die", "dava", "partial", "round d", "curly d" or simply "d", used to denote the following:

• A partial derivative, such as $\frac{\partial z}{\partial x}$ that would be read as "the partial derivative of z with respect to x".
• The Jacobian, $\frac{\partial(x, y, z)}{\partial(u, v, w)}$.
• 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 Dolbeault operator on complex differential forms.

One of the first known uses of the symbol in mathematics is by Marquis de Condorcet from 1770, who used it for partial differences. The modern partial derivative notation is by Adrien-Marie Legendre (1786), though he later abandoned it; Carl Gustav Jacob Jacobi re-introduced the symbol in 1841.

In Unicode character set, this symbol has the codepoint U+2202 and is part of the Mathematical Operators range. In HTML, this symbol has the character entity ∂. In a LaTeX math environment this symbol is inserted via \partial. The symbol resembles a variant of cursive Cyrillic "de".