Abnormal construction means building something in a way that is not normal or usual. Just like how we have rules for playing games, building things also has rules that we need to follow so that everything is safe and works the way it's supposed to.
For example, if we wanted to build a tower that was really tall, we would have to make sure that the bottom of the tower is wider and stronger than the top. If we don't do this, the tower might fall over and hurt someone.
When people don't follow these construction rules, it's called abnormal construction. They might build something in a way that is dangerous or doesn't work correctly. This could be really bad because it could hurt people or damage things around it.
So, it's important to make sure we always follow the rules and build things correctly so that everything stays safe and works the way it's supposed to.