Biochemical Oxygen Demand (BOD) is the amount of oxygen required (in ppm):

 for sustaining life in a water body.

by bacteria to break-down organic waste in a certain volume of a water sample.

for the photochemical breakdown of waste present in 1 $\mathrm{m}^{3}$ volume of a water body.

by anaerobic bacteria to breakdown inorganic waste present in a water body.