In terms of variable types, what defines a constant variable?

A constant variable is fundamentally defined by the property that it cannot change its value after it has been initialized. This aspect is crucial because it establishes the variable as fixed throughout the lifetime of the program. Once assigned, the value of a constant variable remains consistent, offering predictability in the code. This is particularly useful in scenarios where certain values should not be altered, such as mathematical constants (e.g., ∏) or configuration settings that must remain stable.

Other options focus on aspects not directly defining what makes a variable constant. While memory allocation at compile-time is relevant for certain types of variables, it does not inherently define a constant. Similarly, memory size is unrelated to the concept of being a constant; constants can vary in size depending on their data type, just like non-constant variables. Lastly, the ability to hold multiple data types refers to a different concept entirely, typically associated with data structures rather than constants themselves. Thus, emphasizing that a constant variable is characterized by its immutable nature is the key to understanding its definition.