The following, found on the Queer Zine Library site, is a useful definition of zines.
‘Zines are diy publications made by individuals or groups of people rooted in a history of radical political self-publishing. Zines are often motivated by passion and self-expression rather than profit, they are cheap to make and require no skills to create. Zines are a way to document histories and experiences outside of traditional or capitalist publishing.
If you want to find out more about zines, try these useful resources: