Organizations:
Organizations are shared accounts where businesses and open-source projects can collaborate across many projects at once. Owners and administrators can manage members access to the organization's data and projects with sophisticated security and administrative features. You can create more than one organization as per your need.
Organizations includes:
Unlimited membership with a variety of roles that grant different levels of access to the organization and its data
The ability to give members a range of access permissions to your organization's repositories
Nested teams that reflect your company or group's structure with cascading access permissions and mentions
The ability for organization owners to view members' two-factor authentication (2FA) status
The option to require all organization members to use two-factor authentication
The ability to create and administer classrooms with GitHub Classroom
All organizations can own an unlimited number of public and private repositories. You can use organizations for free, with GitHub Free, which includes limited features on private repositories.
Useful Links:
https://docs.github.com/en/organizations/collaborating-with-groups-in-organizations/about-organizations
https://docs.github.com/en/organizations/collaborating-with-groups-in-organizations/creating-a-new-organization-from-scratch
Team:
Team is to group members and manage permission and level of access on different repositories and discussions.
Useful Links:
https://docs.github.com/en/organizations/collaborating-with-your-team/about-team-discussions
https://docs.github.com/en/organizations/collaborating-with-your-team/creating-a-team-discussion