"It is popular in many Arabic countries, as well as Indian and Persian culture where it is called Bande Abru ("Abru" means eyebrow, and "Band" is the thread).
Practitioners use a pure, thin, twisted cotton thread which is rolled over untidy hairlines, moustaches and so on, plucking the hair at the follicle level. Unlike tweezing where a single hair is pulled out each time, threading can remove an entire row of hair, resulting in a straighter line. However, due to a larger area of hair being removed at once, it can be quite painful for some." [Wikipedia]
Unlike waxing, I had to participate in the process. She'd tell me to hold down my eyelid and pull up my upper brow skin- difficult given the pain. If I may be honest, I found this ridiculously painful. I would not do it again and will instead stick to waxing!