Definition - What does External Storage mean?
External storage, in computing terms, refers to all of the addressable data that is not stored on a drive internal to the system. It can be used as a backup, to store achieved information or to transport data. External storage is not part of a computer's main memory or storage, hence it is called secondary or auxiliary storage.
Techopedia explains External Storage
External storage devices are commonly available in the form of flash drives, USB drives, CDs and DVDs. External storage is often used as a form of a backup or for transportation of data from one system to another. External storage allows the user to store information, especially data that is not used frequently, outside the computer’s main memory without much additional cost, since the cost per bit of semiconductors is higher than any external storage device’s price.