Abbreviation of "direct mail" (ダイレクトメール): advertising or promotional mailings sent by companies, including postal mail and email.
新商品についてＤＭが届いた。
A direct mail about the new product arrived.
登録した住所にＤＭを送らないでくださいと書いた。
I wrote that they should not send direct mail to the address I registered.
店から季節のＤＭが定期的に来る。
The store regularly sends seasonal direct mail.
Abbreviation of "direct message": a private message exchanged directly between users on social networks or messaging apps.
詳しい話はＤＭで送ります。
I'll send the detailed information by DM.
知らない人からＤＭが来たので無視した。
I ignored a DM that came from someone I don't know.