Which one of the following refers to a number constant that appears in code without explanation?

A number constant that appears in code without any context or explanation is referred to as a "magic number." This term is used to highlight variables in programming that should ideally be defined with named constants, which enhance code readability and maintainability. Using magic numbers can lead to confusion because it's not clear what the number represents or why it is used at that point in the code. By defining a named constant instead, developers can provide meaningful names that clarify the purpose of the value, making the code easier to understand and modify in the future.

This practice is essential in programming because it leads to cleaner, more understandable code, allowing for better collaboration and maintenance over time. In contrast, other terms like constant, variable, and string literal refer to different programming concepts. A constant is a value that cannot change during execution, a variable is a storage location that can hold different values, and a string literal refers to a sequence of characters enclosed in quotes. None of these terms capture the essence of an unnamed number present in code.