You can load files, like photos and videos, on the USB. You can install apps on the USB. You can't transfer the USB between devices. The USB can be used in addition to your device's storage.

USB is a proprietary non-volatile flash memory card format developed by the Storage Association for as a storage device.

Specification:-

Compatible: All digital devices (Phone & laptop etc)

Speed: Up to 300 MB/s

Storage ability: 4 GB

USB: 3.1 Flash drive

Backward compatible: With USB 2.0