Imagine you and a friend are playing with toys in a room, and suddenly a big, heavy ball comes rolling towards you both. Your friend notices it and shouts, "STOP!" You both freeze, and the ball rolls past you, just missing you by a tiny bit. That was a near miss - it means something dangerous almost happened but didn't actually happen.
In the same way, in places like construction sites, factories or airports, people work with big machines, tools, electricity, and other dangerous things. Sometimes, the people working there might do something wrong, or a machine might not work as it's supposed to, and it could lead to an accident. But if someone notices the mistake or the error, and they shout or signal, the accident can be prevented, and that is called a near miss - a dangerous situation that almost happened but didn't.
However, even though nobody got hurt in a near miss, it is still important to report it to your boss or your supervisor. This helps them figure out what went wrong, and they can fix it so that it doesn't happen again. That's why it's essential to always stay alert and watchful in dangerous situations, so that everybody can stay safe.