OAuth (Open Authorization) is an industry-standard framework for authorization (not authentication!). It allows end users to grant third parties access to their data without sharing their credentials directly with the third party.
In the context of Plaid, OAuth is used to connect to financial institutions. Users temporarily leave Plaid Link to authenticate and authorize data sharing using the institution's website or mobile app. Afterward, they're redirected back to Link to complete the Link flow and return control to the third party application.
You can view the OAuth Institutions page on the dashboard to see the current status of your registration and start the registration process so that your customers can connect to these institutions from your application.