Signing in to several apps with one account, such as a company or Google account, instead of a password per app.
SSO stands for single sign-on. Instead of a different password for every system, an employee signs in once through a central identity provider, such as the company's Microsoft or Google account, and then gets into permitted systems automatically. IT manages it from one place.
Medium and large companies often require it because it simplifies account management: when someone leaves, disabling one account closes access to every system. If you are building an internal tool or a business product, SSO support may be a condition of the deal. See enterprise solutions. Practical tip: for consumers, phone sign-in or Google and Apple sign-in is usually enough. Plan enterprise-grade SSO when business customers start asking for it, and connect it to your roles and permissions model.