What is the BCG matrix?

The BCG matrix is a model to manage the portfolio of products and services/business units a firm offer. Each product, business unit etc. is ranked based of market share and market growth. This creates the following 4 ways to classify each product/business unit: 1. A star: SBU that has a high market share in a growing market. 2. A question mark (or problem child) is an SBU in a growing market, but it does not yet have high market share 3. A cash cow is an SBU that has a high market share in a mature market 4. A dog is an SBUs with low market share in a static or declining market.