bus / busses / buses
The plural of the vehicle, and the kiss.
The plural of the vehicle is buses. Busses is the older plural of bus, and it is also the present-tense verb and the plural noun for kisses: she busses him. For the vehicle, write buses.
Examples
Use Two buses were late.
Use She busses him on the cheek.
Avoid Two busses were late. (If you mean the vehicles.)