The acronym SSO stands for "single sign-on". SSO is a protocol which allows two disparate systems to communicate and permit user access based on shared credentials.
For example, a student may log into their school's website or learning management system and click a link to EdReady (or another provider, a secure content collection, etc.) and be "automagically" logged in to that second system without the need to create an account with a separate username and password. This convenience is known as "single sign-on" or SSO.
When your institution sets up an SSO connection with EdReady, users are identified in EdReady by the name and email address that they use in the school's website. Through the SSO protocol, your institution securely sends the necessary data to EdReady and confirms the user's identity. EdReady then creates an account for the user, or logs the user in if they already have an account that matches the same data.
This system can be used by both students and administrators/instructors. It can also be restricted and combined with regular logins in various ways, for better or for worse.
If you would like more information on setting up an SSO connection with your school's website, please confer with your school's LMS or SIS administrator, and have them fill out this form: https://nroc.org/sso-request
You can read more about the technical aspects of setting up an SSO connection HERE.