An accident is something that happens without a plan, usually something bad.
I dropped the glass by accident and it broke.
An accident is a vehicle crash.
Two people were hurt in a road traffic accident between a car and a motorcycle last night.
Road accidents kill thousands of people each month in the United States, and thousands each week in the world. They injure more thousands each week. The majority involve a car but there are also many bus, truck and bicycle accidents. Aircraft crashes, ship sinkings and other transport accidents also attract much attention.
Injuries from accidents, however, are more numerous at home than elsewhere. They attract less attention because only a few people are hurt at a time.
Often, accidents are investigated so that we can learn how to avoid them in the future. Sometimes by studying an accident we can discover new things, for example penicillin.