This term is shorthand for "electronic magazine." However, this term is a bit misleading. Most e-zines are not as big as the printed magazines you'd buy at a newsstand. They usually have the same amount of content as a printed newsletter. Many people who distribute their newsletters via e-mail call them "e-zines."
An e-zine is an online magazine or an electronic version of a print magazine. E-zines can be independently created, or they can be sponsored by major publishing companies. A magazine is to a journal as an e-zine is to an e-journal. An e-journal tends to be more scholarly than an e-zine.