Final answer:
The act of adding an extra bar of soap to a three-pack and offering it at a special price is referred to as bundling. This practice allows consumers to acquire multiple products or services for a better price and is a common tactic in marketing.
Step-by-step explanation:
Adding an extra bar of soap to a three-pack and offering it at a special price is called a bundle. Bundling is a common marketing tactic where a firm sells two or more products or services as one unit, often at a discounted rate compared to buying the items separately. Examples of bundling include cable companies offering packages with cable, internet, and phone services or computer manufacturers including various software programs with a new computer purchase.