Dethreaded (dictionary)

In a BBS-style chat forum, messages are often organized into threads. A top-level post starts a thread and its replies are contained in the thread beneath it. It is generally considered good manners to keep your replies within the thread to which you are replying.

When someone posts a new top-level post which is actually a reply to an already-existed thread, that message is said to be dethreaded. This is typically considered bad manners, and even against the rules or guidelines in some sites. (On BoyChat, dethreaded messages are against the guidelines unless the original thread has progressed so far down the board that there is a risk no one will see the reply.)