It is a little traditional hand-made doll made of white paper or cloth that Japanese farmers began hanging outside of their window by a string. This amulet is supposed to have magical powers to bring good weather and to stop or prevent a rainy day.
Teru teru bōzu became popular during the Edo period among urban dwellers, whose children would make them the day before the good weather was desired and chant "Fine-weather priest, please let the weather be good tomorrow."
Today, children make teru-teru-bōzu out of tissue paper or cotton and string and hang them from a window to wish for sunny weather, often before a school picnic day. Hanging it upside down - with its head pointing downside - acts like a prayer for rain. They are still a very common sight in Japan.
