System Summary reflects the overall performance and status of the system running Oracle DB from CPU and memory perspectives.
Number of CPUs – Total number of CPUs on the system
OS CPU Load - The percentage of CPU capability currently used by all System and User processes
CPU Usage: % of CPU busy (for all processes) and % of CPU busy for user processes
Total Physical Memory: Total memory on the system, one Instance in case of a RAC
Total Free Physical Memory: Total amount of free memory on the instance
System Physical Memory free: % of free physical memory