A direct message, or DM, is a private message sent through a social media platform like Twitter or Instagram. To send a DM, you must be following the person you want to message. The person you want to message must also be following you, otherwise they will not be able to see your DM. When you send a DM, only the person you are messaging will be able to see it. DMs are a great way to have a private conversation with someone without everyone else seeing it.