Additionally, the monitoring probes have a metrics page providing info on each of the probe's metrics.
cdm Metrics - CA Unified Infrastructure Management Probes - CA Technologies Documentation
Memory Usage (%) QOS_MEMORY_PERC_USAGE Percent Total memory usage in percentage
Physical Memory (%) QOS_MEMORY_PHYSICAL_PERC Percent The size of the physical memory used on the system in percentage
Not mentioned but understood, physical equates to RAM, and in addition to physical RAM a system may also have virtual memory.