railfan; trainspotter; railway enthusiast
Familiar, affectionate term for a railway enthusiast, especially one who enjoys trainspotting or photography. Often used among hobbyists.
He goes out railfanning as a train-photography enthusiast every holiday.
Railfans are always gathering at that station.
From 鉄道 (railway) with the affectionate suffix ちゃん, used to refer to railway enthusiasts in a familiar way.