An event which is unplanned, unintended and unexpected. The outcome of this event depends upon the nature of the accident and the forces and energies involved.
An unforeseen or unintended exposure to risk. This may either be to a risk that has not been identified or to a risk that has been identified but not adequately controlled.
Accidents seldom have one single cause. In almost all cases, a number of factors will have contributed to an accident occurring.