Someone obsessed with trains and railways, sometimes to an unhealthy degree, Otaku-like. This is a type especially common in British and Japanese fictional works, which makes sense since both nations in real life have a high population of such enthusiasts. The United States and Germany have a lot of such enthusiasts as well, as do most other European nations, but generally with fewer depictions in popular media. Related hobbies include bus spotting, plane spotting and model railways without significant interest in real trains. See also Cool Train. The Other Wiki also has an article on this.