One sign-in across apps
With single sign-on (SSO), you sign in to your work account and can then open email and project tools without signing in again. A shared sign-in service checks who you are; each app still decides what you may see or change.
Limited access without a password
OAuth lets one app use part of another service with your permission. For example, a scheduling app may read your calendar availability without getting your calendar password. It receives a limited access token instead.
OpenID Connect builds on OAuth to support “Sign in with…” buttons. SSO describes the one-sign-in experience, which may use OpenID Connect or another sign-in system.