A product's life cycle is a graphical representation of how a product's sales and profitability evolve over time, from its launch to the end of its life.
It is generally divided into four phases: introduction, growth, maturity and decline (the end of the product's life).
Managing a product's life cycle is important for companies because it allows them to plan their marketing strategy and adapt their offer to the different phases of the life cycle, in order to maximize the profitability of the product.
Here is a more detailed article (in french) on the subject : Le cycle de vie produit : booster ses ventes à chaque étape