External storage refers to any device or method used to store digital data that is not within the main device. There are several synonyms for external storage, including portable storage, secondary storage, detachable storage, additional storage and removable storage. These terms describe different types of storage that can be used to store data separately from the internal storage of a device. External storage is commonly used to store large files and backup data, and can include USB drives, memory cards, external hard drives, and cloud storage services. It is a critical component of modern computing, allowing users to retain and access data from any location.