A diya, diyo, deya, deeya, dia, divaa, deepa, deepam, deep, deepak or saaki is an oil lamp made from clay or mud with a cotton wick dipped in oil or ghee. These lamps are commonly used in the Indian subcontinent and they hold sacred prominence in Hindu, Sikh, Buddhist, and Jain prayers as well as religious rituals, ceremonies and festivals including Diwali.

An oil lamp is a lamp used to produce light continuously for a period of time using an oil-based fuel source. The use of oil lamps began thousands of years ago and continues to this day, although their use is less common in modern times. They work in the same way as a candle but with fuel that is liquid at room temperature, so that a container for the oil is required. A textile wick drops down into the oil, and is lit at the end, burning the oil as it is drawn up the wick.