1. What does it mean?
디엠 spells out the sound of the English letters DM, usually meaning direct message. 디엠 보내다 and 디엠 주세요 refer to sending or requesting a message outside the public comment thread.
Also written or said as DM, diem
2. The nuance
It describes the messaging channel, not a guarantee that the recipient will respond or keep the contents confidential. Older business contexts can use DM for direct mail instead.
3. Examples
“자세한 모임 장소는 디엠으로 보낼게.”
I'll send the exact meeting place by direct message.
“판매자에게 상태 사진을 디엠으로 부탁했어.”
I asked the seller for photos of the condition by DM.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.