The phrase "to disk" means to save or copy data onto a storage device, such as a hard drive or USB flash drive. This can refer to saving files from a computer or other device directly to the storage medium, or it can mean copying data from one storage device to another. The term comes from the use of physical disks (such as floppy disks or CDs) as the primary means of storing and transferring information before the widespread adoption of digital storage methods.