1.
north exit, north entrance
The exit or entrance on the north side of a building, typically a train station. Japanese stations commonly label exits by compass direction.
北口 means the north exit or entrance, most commonly of a train station. Japanese stations typically label exits by compass direction to help people navigate.
Forms
北 (north) + 口 (exit/entrance, with rendaku from くち)
Station exit set
OTHER ~口 COMPOUNDS:
Usage
Very common when giving directions to meet someone, especially at stations: 「北口で待ってて」 (Wait at the north exit). The area around each exit often has a distinct character — different shops, bus routes, and landmarks.