The "Digit Sum" is a mathematical concept that refers to the total obtained by adding all the individual digits of a number together. For example, the digit sum of the number 123 is calculated as 1 + 2 + 3, which equals 6. This simple operation is often used in various mathematical applications, including number theory and digital root calculations. Digit sums can also be useful in checking calculations and simplifying numbers. For instance, in modular arithmetic, the digit sum can help determine properties of numbers, such as divisibility. Overall, the digit sum is a straightforward yet valuable tool in mathematics.