Biological Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. It's an important indicator of water pollution, particularly from organic waste. The BOD test typically involves measuring the oxygen demand over a set period, usually 5 days (BOD5), at a specific temperature (20°C). A higher BOD value indicates a greater level of organic pollution and potentially lower water quality, as more oxygen is needed to break down the organic material. This metric helps assess the impact of waste on aquatic environments and the effectiveness of wastewater treatment processes.