A lamp made out of clay is known as earthen lamp. These lamps are usually lighted using ghee, Castrol oil, etc., and offered to the Hindu gods in the temples.
In India, earthen lamps are found in Hindu temples. In south Indian temples, thousands of earthen lamps are using to decorate the floor during popular festivals like Shivratri (Hindu Festival).
The above two images of earthen lamps were captured in the temples of Tamil Nadu. In the temples, many stalls sell earthen lamp like these so that the devotees can buy and offer to the god.