Delta

The fourth Greek letter, meaning change or difference in almost every field.

Also known as: Greek letter delta, Delta symbol, Change symbol, δ, Triangle symbol maths

ScientificMathematicalEngineering & technicalStandard profile

Meanings

Delta is the one Greek letter with something close to a consistent meaning across fields: change, difference, or a small amount. Its capital form Δ is the one most people meet, standing for the difference between two values.

Common modern usageVerified fact
In mathematics and physics, denotes a change or difference between two values, written as a capital delta.
Contexts: Mathematics
Common modern usageVerified fact
Is a letter of the Greek alphabet before it is a symbol: what it denotes is fixed by the field it appears in, not by the character itself. The uses below are the documented conventions, not competing definitions.
Contexts: Mathematics
Common modern usageVerified fact
In calculus, denotes an infinitesimally small quantity, in its lowercase form.
Contexts: Mathematics
Common modern usageVerified fact
In algebra, denotes the discriminant of a quadratic equation.
Contexts: Mathematics
Common modern usageVerified fact
In chemistry, denotes heat applied to a reaction, written above the reaction arrow.
Contexts: Mathematics
Common modern usageVerified fact
In geography, denotes a river delta, named for the triangular shape of the capital letter.
Contexts: Mathematics
Common modern usageDocumented interpretation
Is nearly alone among Greek letters in carrying a stable idea across fields: wherever it appears, it usually concerns difference or change rather than an arbitrary named quantity.
Contexts: Mathematics
Historically documentedDocumented interpretation
Gave its name to river deltas, because Herodotus observed that the mouth of the Nile is shaped like the capital letter.
Contexts: Mathematics

Visual description

In its capital form an equilateral triangle standing on a flat base; in lowercase, a rounded loop with a small curved stroke rising from its top.

Symmetry: vertical
Orientation: upright

Visually similar to: General warning symbol
Capital delta is a bare triangle and the warning sign is a bordered one; the resemblance is of outline only, and the two appear in settings that never overlap.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is defined by a current official standard, but multiple independent sources agree.

Sources

Unicode Code Chart: Greek and Coptic (U+0370–U+03FF)
The Unicode Consortium · retrieved 2026-07-30
Authoritative for the character's code point, name and block only. Unicode assigns identity; it does not define what a symbol means in use.
Greek alphabet
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.
Greek letters used in mathematics, science, and engineering
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.
Delta (letter)
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for the widely-agreed uses of the letter across fields and for its history. Not used to assert that any one use is the letter's definitive meaning — no body defines that, and the record says so.

Last reviewed 2026-07-31