Dum Dum (yes, let's all laugh at the name, har har) is an extremely busy junction some distance north of Kolkata's Sealdah station, a funnel of sorts where lines coming from various points throughout the city converge briefly before splitting towards the northeast, north and west. It's also the northern terminus of the city's single-line metro.
Here, one of IR's MEMUs (main-line EMUs, commonly used in medium-distance regional services) pulls into the station with an unidentified service.