"Replace magic numbers" is a programming practice that involves substituting hard-coded numerical values, known as magic numbers, with named constants. Magic numbers can make code difficult to read and maintain, as their purpose is often unclear. By using named constants, developers can improve code clarity and reduce the risk of errors. For example, instead of using the number 3.14 directly in calculations related to pi, a developer could define a constant like PI_VALUE. This approach enhances code readability and makes it easier to update values in the future, as changes only need to be made in one place.