Hello @AMRUTAAMRUTA , are you new to mumsnet ?
the acronyms take a bit of getting use to but list will help.
Anything that starts D is dear
So Dd is either dear dad or dear daughter, Ds is dear son .
Aibu, is am I been unreasonable, it can get a bit sharp tongued on there so tread carful .
https://www.mumsnet.com/i/acronyms