(1) To disconnect a disk drive or optical disc from a computer. When a user selects "eject" to evacuate an optical disc from the computer, the operating system unmounts the medium. ... (2) To remove a disk or tape cartridge from the drive.

What happens when you unmount a drive?

Unmounting a disk makes it inaccessible by the computer. When a disk is mounted, it is active and the computer can access its contents. ... Since unmounting a disk prevents the computer from accessing it, there is no risk of the disk being disconnected in the middle of a data transfer.

What does unmounting mean?

"Unmounting" means the OS gives up control of the SD card so that other processes, like copying files to your PC and back can access the SD card.