Secondary storage refers to any storage device or medium where data is stored for long periods of time, or for backup purposes. It is commonly known as backup storage or auxiliary storage. Other synonyms for secondary storage include external storage, removable storage, and archival storage. External storage typically refers to a storage device that is connected to a computer externally, such as a USB device or an external hard drive. Removable storage is storage that can be removed from a device, such as a CD or a memory card. Archival storage, on the other hand, is storage that is specifically designed for long-term storage and preservation of data, such as tape drives or optical discs.