Which of the following is not a characteristic of a function?

A function is a fundamental concept in programming that encapsulates a block of code designed to perform a specific task. One of the core characteristics of functions is that they can be called multiple times; this allows for code reusability and organization. Additionally, functions can accept parameters, enabling them to operate on varying inputs and produce different outputs based on those inputs. They can also be defined within other functions, allowing for more complex behaviors and hierarchies within code structures.

While many functions are designed to return a value, it is not inherent to all functions. Functions can also be created specifically to perform actions without returning a value, such as modifying a global variable or printing output to the console. Therefore, the statement that a function always returns a value is not universally true and distinguishes itself from the other characteristics, making it the identified option that does not describe a function.