envelope icon meaning

[Boatman]

What do all the different "envelope icons" to the left of the thread names mean? I can't seem to find that described anywhere.

[monogodo]

http://www.bikeforums.net/images/statusicon/thread_new.gif = a new thread you have not read, or a thread with a new reply in it.
http://www.bikeforums.net/images/statusicon/thread_dot_new.gif = a new reply in the thread, and you've replied in it at some point.
http://www.bikeforums.net/images/statusicon/thread.gif = no new replies in the thread since your last visit, and you have not replied in it.
http://www.bikeforums.net/images/statusicon/thread_dot.gif = an old thread that you've replied to with no new posts since your last visit.
http://www.bikeforums.net/images/statusicon/thread_hot_new.gif = a hot thread with new replies since your last visit.
http://www.bikeforums.net/images/statusicon/thread_hot.gif = a hot thread, with no new replies since your last visit, and you haven't replied in it.
http://www.bikeforums.net/images/statusicon/thread_dot_hot.gif = a hot thread that you've replied to.

[Roody]

What is a "hot thread"?

[monogodo]

A "hot thread" is a thread which is popular, generally one that has over a certain amount of replies in it. I don't know what the post threshold is, or if they're required to be made within a certain time frame or not.