Kaparot (also known as Kaparos) is an ancient Jewish folk custom that is still performed by some (though not most*) Jews today. The tradition is connected to the Jewish Day of Atonement, Yom Kippur, and involves whirling a chicken above one’s head while reciting a prayer. The folk belief is that an individual’s sins will be transferred to the chicken, thereby allowing them to begin the New Year with a clean slate.
Not surprisingly, Kaparot is a controversial practice in modern times. Even among Jews who practice Kaparot, nowadays it is common to substitute money wrapped in white cloth for the chicken. In this way Jews can participate in the custom without bringing harm to an animal (the text and additional details can be found here).
* More precise – only a small minority still performs the Kaparot custom, mainly in Orthodox circles.