on Mac OS X using Memory Clean, I can behold this memory usage stats chart:
While the meaning of active and free seems to be clear, what do "wired" and "inactive" memory refer to?
Wired memory is pretty much memory that the operating system has taken control of and wont let anyone else have. So the system takes what it needs and holds it. And Inactive memory is memory that a program has recently used but is not currently using. This memory sometimes allowes functions that repeat in process to run better. Source