D is the fourth letter
Letter (alphabet)
A letter is a grapheme in an alphabetic system of writing, such as the Greek alphabet and its descendants. Letters compose phonemes and each phoneme represents a phone in the spoken form of the language....

 in the basic modern Latin alphabet
Basic modern Latin alphabet
The International Organization for Standardization basic Latin alphabet consists of the following 26 letters:By the 1960s it became apparent to the computer and telecommunications industries in the First World that a non-proprietary method of encoding characters was needed...


The Semitic letter Dâlet may have developed from the logogram
A logogram, or logograph, is a grapheme which represents a word or a morpheme . This stands in contrast to phonograms, which represent phonemes or combinations of phonemes, and determinatives, which mark semantic categories.Logograms are often commonly known also as "ideograms"...

 for a fish or a door. There are various Egyptian hieroglyphs that might have inspired this. In Semitic, Ancient Greek, and Latin, the letter represented /d/; in the Etruscan alphabet the letter was superfluous but still retained (see letter B
B is the second letter in the basic modern Latin alphabet. It is used to represent a variety of bilabial sounds , most commonly a voiced bilabial plosive.-History:...

). The equivalent Greek letter is Delta, ⟨Δ
Delta (letter)
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 letter Dalet...


The minuscule (lower-case) form of ⟨d⟩ consists of a loop and a tall vertical
Vertical direction
In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...