The purpose of organizations is to make it easier to manage several people working on different apps on Bitrise. Organizations can own an unlimited number of apps, and Organization owners can assign Organization members to work on different apps as they see fit.
Organizations consist of groups: Organization owners can create groups and decide which members belong to which groups. A given group can be assigned to work on an app: all members of the same group will have the same level of access to the app.
Organizations can take advantage of SAML Single Sign-On: we have guides for setting it up with several major identity providers.