Twitter – Understanding the Underscore (@_) Symbol

Direct messages, commonly referred to as simply DMs, are one of the only parts of Twitter that are private.

Introduction

Basically, direct messages are messages you send directly to another Twitter user; no one else can read them, except for the recipient.

However, the user you send a DM to has to follow you on Twitter. This requirement was enacted to decrease the amount of spam on Twitter.

Sending a direct message

There's a few ways to send a direct message:

• You can send one from the main What's Happening? textbox in the Twitter web interface. To do this, you type: d username message or dm username message: username is the name of the user you're sending the DM to, and message is your message.
• You can DM someone by going to their profile page and selecting Direct Message from the Actions button (next to the Lists button).
• You can hover over a user's profile picture in the timeline/inbox and select Direct Message from the Actions button.
• You can go to the Direct Messages tab on the Twitter home page (after you log in) and select a user. Once you do so, you can write a message as usual and click Send.

Difference from @ replies

In your question, you also asked how direct messages are different from posting @username ... on Twitter.

The @username style is known as an @ reply. You can use it to reply to someone's tweet or just say something to them (not to a specific tweet).

They are quite different from DMs:

• The user you @ reply to does NOT have to follow you.
• @ replies are NOT private. They are visible to everyone, unless your tweets are protected (private).

Hope that helped!

Hit ? for a list of those shortcuts available in twitter.com.