Metadata in various forms pervades our institutions, technologies, and daily lives. Metadata is a distinct focus of academic research and professional practice for many people within the library and information sciences (LIS). This article is an exploration of the concept of "metadata." It presents a high-level introduction to the topic with analysis of key research problems and practical challenges. The paper discusses varying understandings of what "metadata" means, the origin and evolution of metadata as an important topic within information and data fields, and the central characteristics of that which gets called "metadata." Metadata can be understood as both process and product and can result from both human effort and computational techniques. Given the central role metadata have in the establishment of knowledge, evidence, and truth, it is necessary for researchers and professionals within LIS to think critically about our metadata practices and systems.
