noun
Seishun 18 ticket; seasonal unlimited local train pass
A special discounted railway ticket sold by JR during school holiday periods, allowing five days of unlimited travel on local and rapid JR trains (excluding Shinkansen and limited express trains). The name 'Seishun 18' (Youth 18) is a brand name; it can be used by anyone regardless of age.
春休みに青春18きっぷを使って日本中を旅した。
I traveled all over Japan using a Seishun 18 ticket during spring break.
青春18きっぷは普通列車しか乗れないけど、とてもお得だ。
The Seishun 18 ticket only allows travel on local trains, but it's a great deal.
The name combines 青春 (youth) and 18 (the age of majority in Japan, symbolizing youthful freedom) with きっぷ (ticket). It was introduced by JR in 1982 as a seasonal discount pass.