What is a constant in programming?

In programming, a constant is defined as an identifier that holds a value which cannot be modified during the execution of a program. This means once a constant is assigned a value, that value remains fixed throughout the lifetime of the program, ensuring that it cannot be inadvertently changed by later operations or functions. This is particularly useful for maintaining values that should not vary, such as mathematical constants like π (pi), or configuration settings that should remain stable throughout the execution of the program.

Using constants helps improve code readability and maintainability, as it clearly indicates to anyone reading the code that certain values are intended to stay the same. Additionally, many programming languages provide mechanisms to define constants to differentiate them from regular variables, reinforcing their unchangeable nature.