The first departure of the day (e.g., the first train or bus); the earliest scheduled service.
始発の電車で通勤している。
I commute on the first train of the day.
始発は午前5時15分発です。
The first departure is at 5:15 AM.
今日は遅れたくないから始発に乗るつもりだ。
I don't want to be late today, so I'm going to take the first train.
Departing from the originating station/stop (i.e., starting from the route's origin); the place where a service begins.
このバスはここが始発なので座席に余裕があります。
This bus starts here (it's the origin), so there are plenty of seats.
始発駅から乗ったので座れた。
I got a seat because I boarded at the origin station.