"MEM and SWP: Amount of memory and swap space that is available and where it's allocated. vmcom and vmlim show how much virtual memory space is committed and what the limit is.
"DSK: disk utilization. avio shows the average number of milliseconds per request.
"NET: Network utilization for the TCP layer ("transport"), the IP layer ("network") and each interface.
"All of these use color to indicate if there are any problems."