The principle that a security architecture should be designed so that each entity is granted the minimum system resources and authorizations that the entity needs to perform its function.
See the following for more information:
NIST SP 800-171 Rev. 2.
NIST SP 800-12 Rev. 1 under Least Privilege.
A security principle that restricts the access privileges of authorized personnel (e.g., program execution privileges, file modification privileges) to the minimum necessary to perform their jobs.
See NIST SP 800-57 Part 2 under Least privilege for more information.