What is the "O" of Ag2O (silver (I) oxide)? Is it an O2-?

Silver oxide is two silver atoms and one oxygen atom bonded together into a molecule of silver oxide.

When oxygen atoms are not bonded to something else, they bond together in pairs forming molecules of O2.

According to the chart about ions AG2O is 2 silver ions and one oxygen ion. I hope this helps

Yes. The compound Ag2O can be written as Ag-O-Ag. Compare H2O = H-O-H.