noun
Refers to the physical gate or barrier where tickets are checked, typically at train stations. The word 'wicket' is an older or less common equivalent.
改札口で切符を通してください。
Please insert your ticket at the ticket gate.
改札 refers to the act of ticket inspection or the ticket gate area in general, while 改札口 specifically means the gate or entrance/exit point.
Compound of 改札 (ticket inspection) and 口 (opening, entrance). The exact historical derivation is straightforward from these components.