A zine is...
You can also find the entry on "Zines" in the St. James Encyclopedia of Popular Culture (Ed. Sara Pendergast and Tom Pendergast. Vol. 5. Detroit: St. James Press, 2000. p 228-229. C2000 Gale Group, C2005 Gale, C2007 Gale, Cengage Learning).
You may want to check out some of Barnard College's extensive information and links on zines:
What is a zine/What isn't a zine?
Jenna Freedman, the zine librarian at Barnard College, offers a more comprehensive definition
Zine Genres An overview of popular kinds of zines, from the Barnard Zine Library