Chemical oxygen demand, which is commonly abbreviated as COD, is an indirect method of determining organic compounds in water. Not only COD is engaged with decomposition of organic matter, but also, it relates with the oxidation of inorganic chemicals (ammonia and nitrite). It is explained as the capacity of water, to consume dissolved oxygen during both of the cases.
BOD is the abbreviation of biological oxygen demand in water. It is also called as biochemical oxygen demand. Before moving in to a deep discussion about the topic, it is better going through some of the important concepts regarding water quality