System Resources???

When you right click on My Computer, select properties and then select the Performance tab you’ll see ” System Resources”. What exactly does that % refer to. I know that it’s more than just availible RAM, because several memory manager apps will all tell me that at any given time I only have anywhere from 3 to 15 MB of RAM “free”, yet System Resources are at 80%+. So what does it refer to? This applies to specifically to Win 98SE, but is the same for Win 98, and Win 95.