1. An exception is an instance of the Throwable type that represents a exception event in a program. When an exceptional event happens, the normal flow of a program can't be completed and this case requires special handling.
2. An expression is a combination of variables and operators that returns a new value.
3. Exception handling consists of a special code block that should be executed when an exceptional event occurs.
4. A checked exception is a type of exception in Java that forces a developer to handle an error that has occurred.