A secondary file is a type of data storage that contains information not essential for the primary operation of a system but still useful for various purposes. These files often support the main data files by providing additional context, backup, or supplementary information. Examples include logs, archives, and temporary files. In many computer systems, secondary files can be used for tasks like data recovery, analysis, or reporting. They help maintain the efficiency of the primary files by offloading less critical data. Common formats for secondary files include CSV, XML, and JSON, which are widely used for data interchange.