Digital roots are a mathematical concept used to simplify numbers. To find the digital root of a number, you repeatedly sum its digits until you arrive at a single-digit number. For example, the digital root of 987 is calculated as 9 + 8 + 7 = 24, and then 2 + 4 = 6. This process is often used in number theory and can help in various applications, such as checking calculations or understanding properties of numbers. Digital roots are also related to modular arithmetic, specifically mod 9, since the digital root of a number is equivalent to that number modulo 9.