What is the unknown folder named .Trash-1000 in pendrive or hard disk?

Have you deleted a file from the USB drive? It has been observed in Linux that when you delete a file, you need to empty the trash on your desktop. Failing to do so will send the deleted files to the folder named .Trash-1000.

If you cannot recover the space so occupied, only option left is to reformat.

You may follow the method mentioned here below too. Being a person not much confident with technical matters, I got this from some other source.

The trash file could be a hidden directory. You may need to enter the following command
cd /media/userName/flashDrive
This will take you to the directory of your drive.
Now enter,
ls -al to find all directories. You should find the directory there. If you do, enter,
sudo rm -r .Trash-1000/.
This should free up your space.

Trash folders are operating system specific. For example Linux and UNIX have this procedure of keeping the deleted data into the "Trash" folder that ends with some unique number. So when you connect the USB drive and delete some content from it, then that goes into numbered trash folder.

Permission for such folder are set on Linux or UNIX based operating systems like (Ubuntu and Apple)and won't be able to delete using Windows operating system. Only drive format option deletes those folders.

If you're on Linux and wish to delete those folders then use following command:

sudo rm -rf ./Trash-1000/

However you can't use any PowerShell command on Windows to delete those files. You can only format the drive.

On the other hand the Windows does not have the file permission set for the files deleted and it doesn't keep it locked. So you can delete "Windows" specific trash folders from any operating system.

If you want to permanently delete the files and don't want to get them listed in Trash folder. In such case use the "SHIFT+DELETE" on any operating system, then this should delete any folder and file from your computer.

By default Ubuntu doesn't have the SUDO permission set for deletion, so it keeps the "trash" folder to keep the log of deleted files.