Transfer learning allows machine learning models to recognize and apply knowledge learned from previous tasks or domains to new related tasks or domains. It involves identifying commonalities between tasks or domains and transferring knowledge, such as feature representations or model parameters. Common transfer learning approaches include instance-based methods that reweight source domain data, feature-based methods that learn shared feature representations, and parameter-based methods that learn shared parameters across related tasks. The goal is to leverage labeled data from source tasks or domains to improve learning on a related target task or domain with few or no labels.