An exception is thrown by Java when a **runtime error** is encountered. The exception provides information about what kind of error occurred. For example: * An `ArithmeticException` is thrown when your program tries to divide by 0. * An `IndexOutOfBoundsException` is thrown when your program tries to access an index that is out of bounds (for example `str.charAt(-1);`, since there is no such thing as the -1 index).
