What is the meaning of “In Proceedings Of ...”?
When it comes to conferences, if there were submitted papers, and they were published as a volume, that volume is called the proceedings. 

A paper that was published in the proceedings must have been accepted by the conference. 

Sometimes the proceedings are published as a standalone work, and sometimes they are published as a special issue of a journal.

It should be noted that some societies publish a journal that has "Proceedings" in the title, such as the "Proceedings of the National Academy of Sciences" or the "Proceedings of the Royal Society". These should be distinguished as standalone journals and not confused with the proceedings of a conference.