Going towards the west, or leading towards the west. It is a practical, sign-and-timetable word rather than a conversation word: you see it on trains, buses, planes, roads and traffic reports. "The westbound train" is the train heading west; "westbound traffic" is the cars going west; "the westbound lanes" are the lanes for cars travelling in that direction. It works both as an adjective before a noun (a westbound flight) and, less often, as an adverb after a verb (the truck was heading westbound). Two things are worth noticing. First, this word belongs to a whole small family built the same way — *eastbound, northbound, southbound*, and also *inbound* and *outbound* — so once you have one, you have them all. Second, it describes direction of travel, not position: a westbound platform is not a platform in the west, it is the platform where you stand to go west. That difference matters a lot when you are actually standing in a station in a strange city trying not to get on the wrong train.