Interrail is a travel pass that allows individuals to explore multiple countries in Europe by train. It is available to residents of Europe and offers unlimited travel on most trains across participating countries for a set number of travel days within a specific period. Travelers can choose from various pass options, including the Interrail Global Pass, which covers 33 countries, or the Interrail One Country Pass, which focuses on a single country. This flexibility makes it a popular choice for those looking to experience diverse cultures and landscapes throughout Europe.