single user mode

Single user mode is a mode in which a multiuser computer operating system boots into a single superuser. It is mainly used for maintenance of multi-user environments such as network servers. Some tasks may require exclusive access to shared resources, for example running fsck on a network share. This mode may also be used for security purposes - network services are not run, eliminating the possibility of outside interference. On some systems a lost superuser password can be changed by switching to single user mode, but not asking for the password in such circumstances is viewed as a security vulnerability.
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(n.) A mode that allows a user to log in to a system as superuser and perform administrative tasks without interference from other users.

"single user mode" in 月刊Linux magazine

A state in which only one user can access a resource. Both SQL Server instances and individual databases can be put into single-user mode.