This is the applications private working set memory usage that is updated at 5 second intervals.
If this value is displaying 0, then follow this procedure to rebuild the performance counters for your system as they are corrupted.
Click Start, type cmd, right click cmd.exe, and select Run as administrator. At the prompt, type lodctr /r and press ENTER. This will rebuild the performance counters for your system.
If this fails with the result message Error: Unable to rebuild performance counter setting from system backup store, error code is 2, then try this in the Command window:
C:\windows\SysWOW64> lodctr /r
You should get a results message Info: Successfully rebuilt performance counter setting from system backup store