Apple Mac Macbook OSX Memory Management

• Wired memory is memory being used by the core processes of the system, and cannot be reclaimed.
• Active memory is memory being used by user processes (primarily applications).
• Inactive memory is memory that was once active, but is now up for grabs should anything need it (OS X is "lazy" with it's memory management and does not de-associate it until needed).
• Free memory is "unassociated" memory that can be used at any time.

Wired + Active + Inactive + Free = the amount of RAM your computer has. The total memory being used at any given time is Wired + Active memory. And the amount of unused memory is Inactive + Free memory.