Delta (upper case Δ, lower case δ) is the fourth 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:
Deltas are the second lowest caste in Aldous Huxley's dystopic satire Brave New World.
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.