What does Oxidizable matter oxygen mean?

May 2019
BS EN ISO 3696, in page 10 a table, shows the requirements for different grades of water. This table mentions a term, Oxidizable matter oxygen. I know what BOD (biological oxygen demand) and COD (chemical oxygen demand) are, but I don't have clear idea about oxidizable matter oxygen. I am ashamed of my ignorance. I searched this term in net, but I didn't find any information that satisfies me. Would anybody like to discuss this term? I have found the following formula from this link (https://bit.ly/2W1Ol5N).
oxidizable material (Mat O) = (2 * BOD5 + COD) / 3
BOD5 = Biochemical Oxygen Demand for 5 days.
COD = Chemical Oxygen Demand.

I would like to attach the screen shot of that table.