Software Architect's Handbook

Retain

Some applications either cannot be migrated to the cloud or an organization may make a decision to not migrate them. In these cases, you will simply be retaining the application in its current environment. There are a number of reasons why an application may simply be retained. There may not be a business justification for moving an application to the cloud. For example, the cost of migrating to the cloud might be too high given the expected benefits.

Organizations that want a hybrid cloud will retain some of their applications in their on-premises infrastructure. In a hybrid approach, some applications will be migrated while others will remain hosted on-premise.