What is the phonetic alphabet term for the letter "D"?

The phonetic alphabet term for the letter "D" is "Delta." This term is used in aviation, military, and other communication fields to ensure clear and unambiguous verbal communication, particularly in noisy environments or over radio transmissions. The use of standardized phonetic terms helps prevent misunderstandings that may arise from similar-sounding letters.

Other terms such as "Bravo," "Alpha," and "Echo" correspond to different letters in the phonetic alphabet, specifically B, A, and E respectively, each with its own designated word. "Delta," however, specifically represents the letter "D," making it the correct choice for this question.