The term "su" is a command used in Unix and Linux operating systems that allows a user to switch to another user account, typically the superuser or root account. This command is essential for performing administrative tasks that require higher privileges than those granted to a standard user. When a user types "su" followed by a username, they are prompted to enter the password for that account. If successful, the user gains access to that account's environment and permissions, enabling them to execute commands that may be restricted for regular users. This is particularly useful for system maintenance and configuration tasks.