Mounting is a process by which the operating system makes files and directories on a storage device available for users to access via the computer's file system.

What does unmount an SD card mean?

Whatever device you put an SD card into, you'll need to mount it, which means the SD card becomes readable by whatever device it's in. ... When you unmount it, the SD card disconnects from your device. If you don't mount an SD card on your Android device, it won't be readable by your device.

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.