n. 1. A person who knows how a complex piece of software or hardware works (that is, who groks it); esp. someone who can find and fix bugs quickly in an emergency. Someone is a hacker if he or she has general hacking ability, but is a wizard with respect to something only if he or she has specific detailed knowledge of that thing. A good hacker could become a wizard for something given the time to study it.
2. A person who is permitted to do things forbidden to ordinary people; one who has wheel privileges on a system.
3. A UNIX expert, esp. a UNIX systems programmer. This usage is well enough established that 'UNIX Wizard' is a recognized job title at some corporations and to most headhunters.