A DM typically refers to a direct message that is sent on Twitter.
The DM is a privately sent message to another user while using the popular social media network.
DM’s are appealing because they are private, so other users cannot see them, and they also no longer have a character restriction that a Tweet does.
A DM used to have a 140 character limit but the company decided in 2015 that it would remove the character limit in order to make it a better tool to use for businesses people.