The BCG growth-share matrix is a portfolio planning model developed in the 1970s. It classifies businesses based on their market growth rate and relative market share. There are four categories: stars (high growth, high share), cash cows (low growth, high share), question marks (high growth, low share), and dogs (low growth, low share). The matrix is used to analyze how much cash each category generates and determines how to allocate resources for maximum return. It helps identify businesses that need investment or can generate profits but has limitations in only using two dimensions and definitions of market.