Office 365 Hybrid Migration is a manual method in which source and target remain in an environment with end to end connection. Using Hybrid Migration, On-premises or Exchange to Office 365 migration and vice versa, can be done. It provides secure connections between On-premises and Office 365 accounts and benefits users by providing integrated control for on-premises and Office 365 accounts. It has some limitations too such as compulsion of Azure Active Directory and Office 365 password syncing as well as a proper know and how is a must to execute this properly.

For more info - Office 365 Hybrid Migration