extra service; relief service; interim service
Refers to an additional or temporary transport service (bus, train, flight, etc.) scheduled to handle increased demand, special events, or disruptions.
Extra services will be operated for the fireworks festival.
A relief bus service was provided on the line suspended due to the typhoon.
増発 means increasing the number of services (e.g., trains, buses) on a regular schedule, whereas 臨時便 implies a temporary, often one-off, extra service.
定期便 is a service that runs on a fixed, regular schedule, whereas 臨時便 is a special or extra service added outside the normal schedule.
Compound of 臨時 (temporary, extraordinary) and 便 (service, transport). The reading is standard on'yomi.