It's chalk that you can use to temporarily "dye" your hair. I used to see young girls in town with a streak of teal, pink and/or purple in their hair and I wondered if they were individually dying just these pieces of hair with several colors. I didn't know until recently that it is just a chalk that washes out. There are lots of videos on Youtube to show you how to do it. It's kind of neat, but I imagine it's a messy process.