The correct distinction lies in the definition and source of these functions. Built-in functions are those that are included in the Python programming language as part of its standard library. These functions, such as print(), len(), and range(), are readily available for use without any additional setup, allowing programmers to perform common tasks efficiently. On the other hand, user-defined functions are custom functions created by programmers. They can be tailored to specific needs or tasks that are not covered by the built-in functions.
This differentiation is crucial because using built-in functions often results in consistent performance and reliability, as they have been optimized and tested as part of the Python distribution. User-defined functions provide flexibility and allow programmers to implement functionality that is unique to their applications. Together, both types of functions enhance the programming experience, enabling both general and specific problem-solving.