Platform or track number 2 at a train station; commonly used in announcements and directions for boarding.
次の快速電車は２番線から発車します。
The next rapid train departs from platform 2.
改札を出て左に曲がると２番線の入口がありますよ。
If you leave the ticket gate and turn left, you'll find the entrance to platform 2.
掲示板で２番線の発車時刻を確認した。
I checked the departure time for platform 2 on the display board.