The humerus is the long bone in your upper arm, from the shoulder down to the elbow. You have one in each arm. Doctors and biology teachers use the word; in ordinary talk most people just say 'the bone in my upper arm'. If you fall on that arm, this is often the bone that breaks. Though actually, people mix it up with humorous (funny) all the time, because they sound almost the same — they are not related at all. One is a bone with a Latin name; the other is about jokes.