Going toward the north, or built to carry people that way. A northbound train is the one heading north; a northbound lane is the side of the road for traffic going north. You can use it before a noun (the northbound bus) or after a verb (we were northbound on the motorway). Signs, traffic reports, and travel talk love it. Though actually -bound here does not mean “tied up”; it means “headed for.” The same pattern gives southbound, eastbound, and westbound. In Taiwan, 北上 often means “going toward Taipei / the north of the island,” which is close in spirit: not a place name, but a direction of travel. Opposite of southbound.