What letter represents delta?

The letter that represents delta is D in the Latin alphabet and Δ, δ in the Greek alphabet. In the Greek alphabet, delta is the fourth letter, coming after alpha, beta, and gamma. The uppercase form is written as Δ, which looks like a triangle, and the lowercase form is written as δ, which looks like a small rounded loop with a tail. This triangle shape is why the word delta is used in geography to describe river deltas, which often form a triangular shape. In the NATO phonetic alphabet used by the military, aviation, and police to spell out letters clearly over radio, Delta represents the letter D. So if someone says Delta, they mean D. In mathematics and science, the uppercase Δ is used to represent change or difference, such as Δx meaning change in x, while lowercase δ is used in calculus to represent a very small change or in chemistry to represent a partial charge. The Latin letter D is derived from the Greek delta, which itself came from the Phoenician letter dalet meaning door. So depending on context, D, Δ, and δ all represent delta.