Microsoft Teams allows people external to the tenant, “guests” to be added to the team. This is called “guest access”. Guest access is different from “external access” (previously called federation), where a user on tenant A can have a 1:1 chat, voice or video call to a user in tenant B. By default, guest access…
— Read on tomtalks.blog/2020/04/controlling-microsoft-teams-guest-access-on-a-per-team-basis/