In computer and Internet phrases there are multiple definitions for the DM abbreviation, including the following:
(1) On the Twitter site (a free social messaging tool), DM is short for direct message, and it is used to send a private tweet (Twitter update) to a person you are following. You can view DMs from the Messages tab of your Twitter profile. You can also choose to receive email notification of new messages.
Direct messaging, or DM is used on other social media sites and services, such as Facebook or Discord, and the phrase is often used in place of the abbreviation PM (private message).
(2) Short for deathmatch, DM is a type of game play mode found in first-person-shooter games.