What is a characteristic of a constant in programming?

A characteristic of a constant in programming is that it is defined only once. This means that once a constant is assigned a value, it cannot be altered throughout the program's execution. Constants are utilized to maintain fixed values that are essential for the program's functioning, ensuring data integrity and preventing accidental modification of crucial values.

In many programming languages, defining a constant typically involves using specific keywords or conventions that signal to the compiler or interpreter that the assigned value should remain unchanged. This characteristic helps in creating more readable and maintainable code since developers can see that certain values are intended to stay the same and won't be modified inadvertently.

The other aspects mentioned do not align with the properties of constants. For example, a constant does not allow its value to change, it cannot store multiple data types in a single declaration, and it is not limited to being a string; constants can represent various data types such as integers, floats, or booleans depending on the programming language's rules.