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Delta (letter)

Greek alphabet
Α α Alpha	Β β Beta
Γ γ Gamma	Δ δ Delta
Ε ε Epsilon	Ϝ ϝ Digamma
Ζ ζ Zeta	Η η Eta
Θ θ Theta	Ι ι Iota
Κ κ Kappa	Λ λ Lambda
Μ μ Mu	Ν ν Nu
Ξ ξ Xi	Ο ο Omicron
Π π Pi	Ϻ ϻ San
Ϙ ϙ Qoppa	Ρ ρ Rho
Σ σ Sigma	Τ τ Tau
Υ υ Upsilon	Φ φ Phi
Χ χ Chi	Ψ ψ Psi
Ω ω Omega	Ϡ ϡ Sampi

Delta (upper case Δ, lower case δ) is the 4th letter of the Greek alphabet. In the system of Greek numerals it has a value of 4.

A river delta is named after the letter delta because it has roughly the triangular shape of the upper-case delta.

The upper-case letter Δ is used as the symbol for:

• A macroscopic change in the value of a variable in mathematics or science.
• Any of the delta particles in particle physics.

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

• A microscopic change in the value of a variable in mathematics or science.
• The Kronecker delta in mathematics.
• The Dirac delta function in mathematics.
• A mark for deletion in proofreading. The usage is said to date back to classical times.

Letters that arose from Delta include the Roman D and the Cyrillic letter De.