Wired: non-pageable memory (usually kernel address space, but can belong to a process if such wiring down is requested by mlock, if mlock is really implemented)
Active: valid mapping (points to an existing filesystem or swap object), referenced by an existing process; pageable
Inactive: valid mapping (points to an existing filesystem object), not referenced by any existing process
Free: invalid mapping (e.g. has never been mapped to anything so far, contains modified filesystem object data, etc)