Excess-3 is a non-weighted code used in digital systems to represent decimal numbers. It is a type of binary-coded decimal (BCD) where each decimal digit is encoded by adding 3 to its binary equivalent. For example, the decimal digit 0 is represented as 0011 in Excess-3, while the digit 9 is represented as 1100. This coding system helps simplify arithmetic operations in digital circuits, as it avoids the need for complex carry operations. Excess-3 is particularly useful in applications like calculators and digital displays, where accurate representation of decimal numbers is essential.