Threading is something that I learned about when I moved to South Asia. I hadn't heard about it before I actually saw one of my friends get it done. It actually originated in Iran and carried over to the rest of Asia pretty quickly and is now even becoming popular in the US.
So what is threading? Well, it's pretty much a method of removing hair. In South Asia, they use it mostly to fix eyebrows and to get off other unwanted facial hair. They use a thread and hold one end in their mouth and use both hands and rip out the hair at the folicle. They can remove a whole row of hair at a time this way. It's pretty crazy and it's supposed to be more painful than waxing. Here's a video of it below:
It's only a short clip, but if you want to see more check out Another Short Threading Video.