By what oosyrag means, it's the main information you see below upon onn launching a debug preview. All your global variables, the cpu/memory loads, etc. It's called System, as noted on the list on the left side of the debugger.
It's also true, monitoring things with System as the main focused debug window will give you significant fps drops. Switch to a different object, such as a sprite or an array and the fps will usually go up instantly, if not after a couple of seconds, jump back to 60 FPS or so.
[quote:p0l6mu7u]So i added a textbox to show fps and cpu % during lan testing, would that be closer to what can be expected?
No, as with the caveat above, a textbox or text object displaying fps will still suffer EVEN if you happen to keep the System view up in the debugger. Also, as for what Ashley said, he means the normal preview mode. It'll have "localhost:xxxxx" instead of "localhost:xxxxx/debug".
Keep mind if you're seeing fps dps while not running System, you may have a bottleneck caused by one of your events and/or event sheets.