100-yen bus; flat-fare 100-yen bus
A bus service where a single ride costs a flat 100 yen, typically within a limited area. The term is wasei-eigo from 'one-coin bus'.
wasei-eigo (Japanese-coined English), from one-coin bus
The 100-yen bus that runs through the city is convenient for tourists.
Let's take the 100-yen bus to the station.
Wasei-eigo from English 'one-coin bus', referring to a bus with a flat fare of 100 yen (one coin).