Merriam-Webster's Advanced Learner's Dictionary:
1bus /ˈbʌs/ noun, pl bus·es also US bus·ses : a large vehicle that is used for carrying passengers especially along a particular route at particular times
[count]
• She boarded a bus in Nashville.
[noncount]
• I usually go to work by bus. = I usually take the bus to work.
• Are you traveling by train or by bus?
- often used before another noun
• a bus driver
• a bus station
• waiting at the bus stop [=one of the places where a bus stops for passengers to get on or off]