The expression "cz + d" represents a mathematical formula where "c" and "d" are constants, and "z" is a variable. In this context, "c" is multiplied by "z," and then "d" is added to the product. This type of equation is often used in algebra to describe linear relationships. In practical applications, "cz + d" can model various real-world scenarios, such as calculating costs or predicting outcomes. For example, in economics, it might represent the total cost C based on a fixed fee d and a variable cost c that depends on the quantity z of goods produced.