A disk that is "write protected" means that the contents of it cannot be altered, deleted or formatted. This prevents unauthorized modifications to the disk and protects the data stored there. Any form of computer storage may use write protection.
Early floppy disks used a hole or notch to institute this feature. Hard drives require an adjustment of software settings to implement the protection. USB flash drives or cards may have a either physical switch on the device's exterior or a software alteration. The term may also be used synonymously with the phrase "read only." Both signify that the data contained therein cannot be tampered with.