The 'delta' 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 letters where the alphabets are a type of writing system consisting of 22 consonant letters only, leaving vowel sounds implicit. The Nile River delta is so named because its shapes approximates the triangular uppercase letter 'delta' (Δ).

The upper case letter 'Δ' can be used to denote a change of any changeable quantity in mathematics and sciences viz., ΔY=y2-y1 or ΔX=x2-x1.The 'delta' is the initial letter of the Greek word 'difference'.The 'Δ' can be used to any of the 'delta particles' in particle physics, where Δ++, Δ+, Δ0, Δ-1 carry electric charges of +2e, +1e, 0e and +1e. In chemistry, the addition of heat in a reaction,'Δ' is used to show the change of the reaction. The 'Δ' is applicable in a major seventh in Jazz music notation. The lowercase letter '𝛿' can be used to denote a change in the value of a variable in calculas; the relative electronegative of different atoms in a molecule, 𝛿- being more electronegative than 𝛿+. The ratios of environmental isotopes, such as 180/160 and D/1H from water are displayed using delta notation. In computer encodings, both upper and lower cases 'delta' are used.

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