A Usb Flash drive is a data storage device that includes flash memory with an integrated USB interface. It is typically removable, rewritable and much smaller than an optical disc.

A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case, which can be carried in a pocket or on a key chain, for example. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. 

There are several errors in Usb Flash Drives. This error is one example. 

"The-file-or-directory-is-corrupted-and-unreadable"

with this error, you can't open or  access any of your files, so before resulting in reformatting your flash drive, try first this method and might save your data.

chkdsk command checks the file system and file system metadata of a volume for logical and physical errors. If used without parameters, chkdsk displays only the status of the volume and does not fix any errors. If used with the /f, /r, /x, or /b parameters, it fixes errors on the volume.