In computer programming, a constant is a variable whose value cannot be changed once it has been assigned. It is a fixed value that remains the same throughout the execution of a program. Constants are often used to represent values that are known and unchanging, such as mathematical constants or configuration settings.

Constants are typically declared with a specific data type and are assigned a value during their declaration. They can be accessed and used in the program just like any other variable, but their value remains constant and cannot be modified after initialization.

Using constants can improve the readability and maintainability of code as it provides a clear indication that a particular value should not be altered. It also allows for easier modification of the value in a single place, making it less error-prone and more efficient.