second-to-last train of the day
Dated term, historically used in contrast with 赤電車 (last train). Now rarely used; modern Japanese prefers 終電の一つ前 or similar expressions.
See also: 赤電車
In the past, the term 青電車 was used to refer to the train just before the last train.
Compound of 青 (blue) and 電車 (train). The color naming likely comes from a system where the last train was marked in red (赤) and the second-to-last in blue (青), but the exact origin is uncertain.