noun
on-train ticket inspection
Refers to the practice of checking passengers' tickets while the train is in motion, rather than at station gates.
この路線では、車内改札が行われることがあります。
On this line, on-train ticket inspections may be conducted.
改札 is a general term for ticket inspection or a ticket gate, while 車内改札 specifically refers to inspection conducted inside the train.
Compound of 車内 (inside a train) and 改札 (ticket inspection).