Medical scientific data are a crucial resource for innovation in the digital and big data era. These data are considered the key drivers of modern productivity. Defining medical scientific data, sharing, and applications are essential for establishing effective data governance and management systems. In the context of Internet and data science, data sharing has become an inevitable trend. This chapter defines key terms related to data and data sharing, standardizes basic concepts, classifies scientific medical data from various perspectives, and summarizes the significance and challenges of data sharing, thereby laying the groundwork for exploring governance theories and practices.