A plural form of 'bus' — more than one bus. Here is the thing to understand: 'buses' and 'busses' are both correct English, but they are not equally common. 'Buses' with one s is the normal, standard spelling everywhere today, and it is what you should write. 'Busses' is an older, less used spelling that you will still find in some American writing and in older books. If you write it, nobody will call it wrong, but it looks dated, and some readers will assume it is a typo. The reason English hesitates is that a one-syllable word ending in a single s usually doubles that s before an ending — gas→gasses (as a verb), quiz→quizzes — but 'bus' is a shortened word (from omnibus) and never fully settled into that rule. Note too that 'busses' is also the third-person form of the old verb 'buss' meaning 'to kiss': 'She busses him on the cheek.' That meaning is rare, so context makes it clear.