Northbound means traveling or moving toward the north. When a train is northbound, it's heading in the direction where compasses point. If you're on a northbound highway, you're driving north, away from the equator and toward the North Pole.

The word often appears on road signs, train schedules, and traffic reports. You might hear that “the northbound lanes are closed for construction” or catch “the northbound subway.” Cities often have both northbound and southbound routes running parallel to each other, like two sides of the same street carrying traffic in opposite directions.

Sometimes people use the word more loosely to mean “going up” or “improving,” as in “sales are northbound this quarter.” But mostly, northbound simply describes physical direction: a northbound migrating bird is flying toward its summer home in the northern regions, just as southbound birds head toward warmer climates when winter approaches.