This video explains single and multi-tenant applications concepts in Microsoft Entra ID (Azure Active Directory).
Helpful links:
Tenancy in Microsoft Entra ID:
https://learn.microsoft.com/en-us/entra/identity-platform/single-and-multi-tenant-apps
Making your application multi-tenant:
https://learn.microsoft.com/en-us/entra/identity-platform/howto-convert-app-to-be-multi-tenant