Migration.
Your organization currently has either Exchange Server on-premises, a thirdparty email system, or another vendor’s cloudbased mail service and you want to move them to Exchange Online before decommissioning their
current system completely.
The result is that only Exchange Online handles messaging for the organization.
Migrations can be either cut-over, which moves the entire organization in one pass, or staged, where the users are moved in batches and there is a temporary coexistence phase.