SSO, or Single Sign-On, lets a user log in once with one set of credentials and get access to many applications. Instead of remembering a different password for every system, an employee signs in one time and reaches everything they are authorized to use.
Fewer passwords means less password fatigue, and it reduces the temptation to reuse the same password across many accounts, which is a major security risk. When SSO is combined with MFA, you get both convenience and a much stronger barrier against a compromised login.
