The document discusses the product life cycle, which includes four main stages: introduction, growth, maturity, and decline. In the introduction stage, the product is new to the market and sales are low while costs are high. The growth stage sees rapidly rising sales as more customers adopt the product. In maturity, sales growth slows as the product reaches most potential customers. Finally, in decline, sales begin to fall as customers switch to newer products. The document outlines strategies for marketing and pricing in each stage of the product life cycle.