An accident happens when something goes wrong without being planned or intended.
When we say something was an accident, we usually mean that it wasn't meant to happen. For example, if you spill coffee on your shirt by mistake, that's an accident. You didn't try to spill the coffee; it just happened. If someone trips and falls, that's often an accident too – they weren't trying to fall over. Accidents can also be when something bad happens without being planned, like a fire in a building. In general, we use "accident" when we want to say that something unexpected went wrong.
Pertaining to accident and not essence; thus, inessential; incidental; secondary.
