The Fama-French data library is a collection of financial data created by economists Eugene Fama and Kenneth French. It provides researchers and investors with access to various datasets, including stock returns, market factors, and portfolio performance metrics. This data is essential for analyzing asset pricing and understanding market behavior. The library includes key factors like size and value, which help explain differences in stock returns. By using this data, analysts can conduct empirical research and develop investment strategies based on the Fama-French three-factor model and other related models.