PokerTracker

In notetracker there is a note that comes up for players [O} which is overall.
Some players have [O} 12 while others have many variaties of numbers, I’ve seen [O} 320.

Can anyone offer some insight as to what these numbers mean after [O]?

It sounds like you're looking at a NoteTracker note -- you can find the definitions on Tools -> NoteTracker. Unfortunately from the information you've given I can't tell you what the note you're talking about does but you should be able to find it in that window.