The first train of the day (the earliest scheduled departure, often from the line's starting station).
毎朝、始発電車で会社に行っている。
I take the first train every morning to go to work.
雪の影響で始発電車が遅れ、駅に人があふれていた。
Because of the snow the first train was delayed and the station was crowded.
始発電車に乗れば座れることが多いので、遠距離通勤の人に人気だ。
Riding the first train often means you can get a seat, so it's popular with long-distance commuters.