Delta (letter) has use mathematics
Change of any changeable quantity, in mathematics and the sciences (more specifically, the difference operator); for example, in  the average change of y per unit x (i.e. the change of y over the change of x). Delta is the initial letter of the Greek word διαφορά diaphorá, "difference". (The small Latin letter d is used in much the same way for the notation of derivatives and differentials, which also describe change by infinitesimal amounts.)
The Laplace operator:Lowercase
The lowercase letter δ (or 𝛿) can be used to denote:A change in the value of a variable in calculus
A functional derivative in functional calculus
An auxiliary function in calculus, used to rigorously define the limit or continuity of a given function
The Kronecker delta in mathematics
The degree of a vertex (graph theory)
The Dirac delta function in mathematics
The transition function in automata
Deflection in engineering mechanics
The force of interest in actuarial science
The chemical shift of nuclear magnetic resonance in chemistry
The relative electronegativity of different atoms in a molecule, δ− being more electronegative than δ+
Text requiring deletion in proofreading; the usage is said to date back to classical times
In some of the manuscripts written by Dr. John Dee, the character of delta is used to represent Dee
A subunit of the F1 sector of the F-ATPase
The declination of an object in the equatorial coordinate system of astronomy
The dividend yield in the Black–Scholes option pricing formula
Ratios of environmental isotopes, such as 18O/16O and D/1H from water are displayed using delta notation – δ18O and δD, respectively
The rate of depreciation of the aggregate capital stock of an economy in an exogenous growth model in macroeconomics
In a system that exhibits electrical reactance, the angle between voltage and current
Partial charge in chemistry
The maximum birrefringence of a crystal in optical mineralogy.
An Old Irish voiced dental or alveolar fricative of uncertain articulation, the ancestor of the sound represented by Modern Irish dh