In Python, all built-in exceptions are instances of a class derived from BaseException. They are generated by the interpreter or built-in functions to report error conditions and typically include an associated value (e.g., a string or tuple) indicating the exact cause of the error. These built-in classes can be subclassed to define custom exceptions, which should derive from Exception rather than BaseException.

URL: https://docs.python.org/3/library/exceptions.html