You probably mean this thread: Anxiety, Panic and Phobias > cant keep living like this. Someone added a few search tags to the thread, is all. They're listed at the bottom of that page:

Tags
anxiety, depression, ocd, phobia, schizophrenia

Where a tagged thread is listed on a forum index page, it'll have a tag icon to the right of the thread title, like this: If you hover your mouse pointer over the icon you should see a list of the tags for that thread.

One of the things tags are good for is that you can use them to search for posts on a particular subject -- that is, if someone has tagged those posts with the subject you're looking for. Here's that feature, on the Advanced Search page. I just tagged this thread too, to reflect what it's about.