Delta (letter)

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Delta (uppercase Δ, lowercase δ) is the fourth letter of the Greek alphabet. In the system of Greek numerals it has a value of 4. It was derived from the Phoenician letter Dalet . Letters that arose from Delta include the Latin D and the equivalent in the Cyrillic alphabet Д.

In Modern Greek it is pronounced = ] = the average change of y per unit x

The Laplace operator:

[\Delta f = \frac + \frac ]

The discriminant of the quadratic equation:

[\Delta = b^2 - 4ac\,\!]

A macroscopic change in the value of a variable in mathematics or science.

Any of the delta particles in particle physics.

As a symbol for defendant in legal shorthand.

The lower-case letter δ is used as the symbol for:

An infinitesmal change in the value of a variable in mathematics or science.
An auxiliary function in Calculus used to rigorously define the limit or continuity of a given function.
The Kronecker delta in mathematics.
The Dirac delta function in mathematics.
Deflection in engineering mechanics
A mark for deletion in proofreading. The usage is said to date back to classical times.

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