Really, that's what it is. It is a self-published publication on pretty much any subject that you wish to discuss, comment on, cartoon, instruct. The possibilities are only limited by the human imagination. I learned about 'zines from a friend who is addicted to making informative 'zines about yoga. I have 3 'zines in my repertoire currently and they are all instructional. One teaches how to knit, one how to purl, and the other how to crochet.
Today I learned about the Seattle Zine Archive and Publishing Project whose claim to fame is that it is the world's largest collection of 'zines. Pretty impressive. My three 'zines will begin their journey to the western United States to join this collection this afternoon thanks to an Etsy order. I am so proud! I wish I could accompany my 'zines there and see this neat space for myself. Actually I have had a hankering to visit Seattle since I watched a travel episode dedicated to this city.
I encourage people to make their own 'zines...http://www.youtube.com/watch?v=q5oD8EyZHOU this links you to a cute little video on how to make a one-sheet mini 'zine. The only thing is it doesn't explain where to place your cover and each consecutive page on the full sheet of paper. Look at the video carefully and see where the artist's cover page is, then each page thereafter is placed going counter-clockwise around the page. You'll figure it out!
Also, here is the info on ZAPP the Zine Archive and Publishing Project http://www.hugohouse.org/zapp