A Zine is a small publication, usually produced by an individual or small group of people. They are usually produced in small batches, often with a handmade original that is reproduced on a photocopier. They are most often stapled but other methods of binding are also used. Zines tend to be focused on a particular interest or theme. Due to the personal and DIY nature of zines and zine-making, they are often produced on an irregular schedule.
Pratt Libraries has several books about Zines that may be interesting if you want to learn more.
(there are others - search PrattCat to find more)
Barnard College has one of the best-known Zine Collections and is a fantastic resource for all things Zine. They have created this wonderful collection of links to a variety of Zine collections in the US as well as some other countries: