A zipper is a sliding fastener. You'll get cold and wet if you don't zip the zipper on your coat during a blizzard.
Zippers are usually made of metal or plastic teeth that fit together as you slide a tab along them. It's common to have a zipper on your coat, jeans, or dress instead of snaps or buttons. Suitcases and sleeping bags are usually closed with zippers too. The zipper was invented in 1917, but it was initially called a "zip." At the time, a zipper was a particular type of boot that zipped closed.