What does C.O.D. mean?

I've reached the end of chapter 9 in the simplified manual. I still haven't start writing any shorthand because I thought I should learn all the theory and be able to read smoothly first.

Anyway there was a term called C. O. D. in lesson 46, what does it mean? I'm guessing that it could be a term commonly used back in the days... Now we have CEO, HOD etc. but I haven't got an idea about that. I would appreciate if someone can give me a tip on this. Thanks.

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