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 ? (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