f2db8a79_OS_X_Tips_Tweaks_and_Tutorials__What_the_data_means
[Subcategory] System Cache [What the data means] 
Reports on the total amount of RAM, in kilobytes, that is being used for the most recently accessed data and programs. Programs and data can be in the system cache even after they have been closed down; the PC looks to the system cache first when opening a program or file, since it can be opened from the cache faster than from the hard disk.
Windows Task Manager – Performance Monitoring Explained | Windows Vista,XP, Linux and OS X Tips,Tweaks and Tutorials
What the data means