The FAIR principles describe how research outputs should be organized so they can be more easily accessed, understood, exchanged and reused. FAIR data, data that's findable, accessible, interoperable, and reusable, is data that follows certain guidelines. This guide has details about those guidelines in more detail.
Why are the FAIR principles needed? The increasing availability of online resources means that data need to be created with longevity in mind. Providing other researchers with access to your data facilitates knowledge discovery, enables reproducibility, fuels new and interdisciplinary research questions, and improves research transparency.