Secondary storage is a type of computer storage that is used to store data permanently for later retrieval. It is also known as external storage or auxiliary storage. The data stored in secondary storage is not immediately accessible by the computer's processing unit and needs to be first copied to the primary storage before it can be used. Some common examples of secondary storage include hard disk drives, solid-state drives, magnetic tapes, optical discs, and USB flash drives. Secondary storage is used to store large amounts of data that cannot fit in primary storage, to backup important files and databases, and for long-term storage of archives and historical records.