Full Disk Encryption (FDE) is a security measure that protects all the data on a storage device, such as a hard drive or SSD. It uses encryption algorithms to convert the data into a format that is unreadable without the correct decryption key. This means that if someone tries to access the device without authorization, they will not be able to view or use the data stored on it. FDE is commonly used in devices like laptops and smartphones to safeguard sensitive information. By encrypting the entire disk, it helps prevent unauthorized access in case the device is lost or stolen. Popular FDE solutions include software like BitLocker for Windows and FileVault for macOS.