JET is short for the Japanese and Exchange Teaching Program. You are hired by the Japanese government to go to public schools (elementary through high school) to be an assistant in the English classrooms. It's basically so the students have a native speaker that they can listen or talk to in order to better improve their English abilities. Here is the URL for it:
http://www.jetprogramme.org/. If anyone is interested in something like that I would be glad to talk to you about my experience so far.