Henna is a common name for completely natural products used for dyeing hair, eyebrows, and drawing patterns on the body. The term itself comes from the name of a shrubby plant, whose leaves are first dried, then crushed and turned into a green powder, which is later used for cosmetic purposes. Henna is most commonly used for natural hair care and dyeing treatments, without damaging the hair.
To get different shades (black, red, brown...) it is usually mixed with other plants (e.g., with the powder of the indigo plant). Read all about henna for hair on the blog.