noun
removable storage
Technical computing term for storage media that can be easily removed from a computer, such as USB drives, external hard drives, or memory cards.
取り外し可能記憶装置にデータをバックアップしてください。
Please back up your data to a removable storage device.
外部記憶装置 is a broader term for external storage, which may or may not be removable. 取り外し可能記憶装置 specifically emphasizes the ability to detach the medium.
Compound of 取り外し (removal) + 可能 (possible) + 記憶装置 (storage device). A straightforward technical term.