Which term represents a value that cannot change once defined in programming?

The term that represents a value that cannot change once defined in programming is a constant. Constants are specifically designed to hold fixed values. For instance, in many programming languages, you can declare a constant using specific keywords (like "const" in C and C++ or "final" in Java). Once this value is assigned, it cannot be altered throughout the program's execution, ensuring consistency and preventing accidental changes.

Constants are especially useful for values that should remain the same, such as mathematical constants (like Pi) or configuration values that should not be modified. Utilizing constants can enhance code readability and reliability, making it clear to other developers that these values are intended to remain unchanged.

The other terms have different meanings: a variable is a value that can change during the program's execution; an identifier is simply a name used to identify a variable, function, or any other user-defined item; and a literal is a fixed value directly represented in the code (like numbers or strings). These distinctions underscore why the term constant is the appropriate choice for defining unchanging values in programming.