A thread on Facebook is a private conversation between two or more people, according to the Facebook Help Center. A thread contains all Facebook emails, chat messages or text messages between the participants. All of your threads are accessible in the "Messages" area of your Facebook account. While Facebook restricts the official definition of "thread" to private conversations, you may also see people on Facebook refer to public conversations and discussions as threads.
Starting a Private Thread on Facebook
To start a private thread on Facebook, you can send a private message, chat message or text message to one or more Facebook users. When you do this, a new thread is automatically saved to your Facebook Messages.
Responding to a Private Thread on Facebook
You can respond to a private thread that includes you by visiting your Facebook Messages, accessible by clicking the "Messages" bookmark on the top-left side of the page when signed in to Facebook and viewing your News Feed. Threads are listed chronologically, with the most recently updated threads appearing at the top. Click a thread preview to view it in its entirety, then enter a new message in the box at the bottom of the thread. Click the "Reply" button to update the thread for all participants to see.
Additional Features of Threads on Facebook
When starting or responding to a thread on Facebook, you can attach a file, picture or video from your hard drive by clicking the buttons below and to the left of the message composing box. You can also click the cell phone icon below and to the right of the box to send the message to the recipients' registered cell phones.
Adding People and Leaving Threads
When responding to a thread, you can add people to the conversation by clicking the "Actions" button above the thread and clicking "Add People." Type their names and click the "Add People" button. You can also leave a conversation, so that you will no longer receive notifications about new messages in the thread; click the "Actions" button and select "Leave Conversation."
Other Definitions of "Thread" on Facebook
On Internet discussion forums, blog comments and elsewhere on the Internet, a "thread" is used to describe any conversation, public or private. On Facebook, people often refer to public conversations as "threads." This applies to comment sections below Wall posts and in discussion topics in Facebook Groups and Pages.