In order to help us keep things more organized, we ask that when posting certain kinds of content (Photos, Videos, News & Blogs, etc) that you add what's called a 'thread prefix' to the thread you're creating:
Clicking on the 'prefix...' input area will bring up a drop down menu giving you a number of thread prefixes to choose from, depending on what kind of content you're trying to post. In this example we'll be posting a video to the forum:
You will now see the prefix next to your thread title:
Continue writing your post and click the Post Thread button at the bottom of the window. Now that your thread has been posted to the forum, you can use thread prefixes to filter different types of content. In the picture below you can see that there are several thread prefixes located along the top of the train hopping forum:
Clicking on any of these in a forum section will filter out any threads that do not have that thread prefix. So, for example, if we click on the videos prefix:
We can now see all the threads in the train hopping forum that have been tagged with the thread prefix 'videos'.
As you can probably tell, this makes it a little easier for folks to find the videos you've posted, or if you're only interested in watching videos (or photos, etc) in a certain forum area.
Finally, you can remove the current filter by clicking the x next to the active filter at the top of the list of threads:
Which prefixes Should I Use?