A Christian religion often called a cult. They are well known for their frequent missionary visits, wherein they knock on your door, armed with pamphlets and magazines. They should not be confused with Mormon missionaries; a distinct difference is that Jehovah's Witnesses will try to tell you that your religion is wrong using their analytical facts.
JW Missionary: So what religion do you belong to?
Me: I'm a Mormon.
JW Missionary: Well, your Book of Mormon contradicts the Bible!
Me: How so?
JW Missionary: Well, we don't have any of them with us right now...