There are four distinct stages in the product life cycle.
1 - Introduction
The market is flat with little growth as products are introduced to it, products are driving low revenue and are likely to be break-even rather than highly profitable.
2 - Growth
There is a rapid growth both in revenue and profits, allowing the firm to reinvest in promotion to drive brand preference of their product.
3 - Maturity
There is no longer strong growth in the market, and the rivalry between firms gets more intense. Firms focus on defending market share and profits, meaning marketing spend is monitored closely as a high spend could easily be copied by competitors reducing profits with few benefits.
4 - Decline
The market is shrinking, making the potential profits for firms lower. Products have to be managed carefully to ensure they remain profitable, such as by cost engineering or outsourcing production. Some firms may choose to remove the product from the market.