Securables are the resources to which the SQL Server Database Engine authorization system regulates access. For example, a table is a securable. Some securables can be contained within others, creating nested hierarchies called "scopes" that can themselves be secured. The securable scopes are server, database, and schema.
The entity that receives permission to a securable is called a principal. The most common principals are logins and database users. Access to securables is controlled by granting or denying permissions, or by adding logins and user to roles which have access. For information about controlling permissions, see GRANT (Transact-SQL), REVOKE (Transact-SQL), DENY (Transact-SQL), sp_addrolemember (Transact-SQL), and sp_droprolemember (Transact-SQL).