Memory terminology in Mavericks Activity Monitory
For each process there is 


Real Memory (always at least as big as Memory)

Total Memory currently consumed by an application (including Virtual pages)

Memory

Memory used in RAM

Purgeable Memory

Memory which can be cleaned by MMU, if another process needs more real memory.



Then, for the system in total


Physical Memory

The amount of RAM installed.

Memory Used

The amount of RAM being used and not immediately available.

Virtual Memory

The amount of disk or flash drive space being used as virtual memory.

Swap Used

The space on your drive being used to swap unused files to and from RAM.

App Memory

The amount of space being used by apps.

Wired Memory

Memory that can’t be cached to disk, so it must stay in RAM. This memory can’t be borrowed by other apps.

Compressed

The amount of memory in RAM that is compressed.

File Cache

The space being used to temporarily store files that are not currently being used.