What is the meaning of Dd?

Abbreviation of day, in two-digit numeric format, as in: dd/mm/yyyy.

A letter of the practical Hadza alphabet, found in interjections only.

abbreviation of du da? (“and you? what about you?”)

abbreviation of dag (“day”), in a two-digit numeric format used for dates

initialism of du då? (“and you? what about you?”)

initialism of du då? (“and you? what about you?”)

The sixth letter of the Welsh alphabet, called èdd and written in the Latin script. It is preceded by d and followed by e.

Source: wiktionary.org