The full form of BOD is Biochemical Oxygen Demand.

Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a water sample at a certain temperature over a specific time period. It is commonly expressed in milligrams of oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often used as a gauge of the organic pollution in effluent, surface water, and wastewater.

• More information can be found at: USGS - Dissolved Oxygen and Biochemical Oxygen Demand