The command "dd" is a utility in Unix and Unix-like operating systems used for low-level copying and conversion of raw data. It can read from and write to files, devices, and partitions, making it useful for tasks like creating disk images or backing up data. The command allows users to specify input and output files, block size, and other parameters. "dd" is often used in system administration and data recovery scenarios. For example, it can clone a hard drive or create a bootable USB drive from an ISO file. Its versatility makes it a powerful tool for managing data at a low level.