A constant is a value that remains unchanged during the execution of a program, whereas a variable’s value can vary throughout the program’s lifecycle.

In programming, a constant is a specific type of identifier whose value remains fixed and cannot be altered once it has been defined. This immutability makes constants particularly useful for values that are utilized repeatedly in your code but should not be modified—either accidentally or intentionally. For instance, the value of $\pi$ in a mathematical computation or the maximum number of students permitted in a classroom within a school management system are examples of values that could be defined as constants.

In contrast, a variable serves as a symbolic name for a memory location where data can be stored. Variables are mutable, meaning that their values can be changed at any point during the execution of the program. They are essential for storing data that may need to be manipulated or updated later. For example, in a program designed to calculate the area of a circle, the radius could be represented as a variable because it can take different values for different circles.

The primary distinction between constants and variables lies in their mutability. Constants are immutable, meaning their value is established at the moment of declaration and remains the same throughout the program’s execution. Variables, however, are mutable, allowing their values to be changed anytime after they have been declared.

When it comes to syntax, the way constants and variables are declared can differ across programming languages. For instance, in Java, constants are typically declared using the ‘final’ keyword, whereas variables do not require a specific keyword. In Python, constants are often denoted by writing their names in all capital letters, although this is merely a convention and not a strict rule enforced by the language.

Understanding the difference between constants and variables is essential for effective programming. This knowledge aids in writing more efficient and error-free code, as well as in comprehending the flow and logic of a program.