Portability means that you can move an application from one host environment to another, including cloud to cloud such as from Amazon Web Services to Microsoft Azure. The work needed to complete the porting of an application from one platform to another depends upon the specific circumstances.
Containers are one technology meant to make such porting easier, by encapsulating the application and operating systems into a bundle that can be run on a platform that supports that container standard like Docker or Kubernetes. But containers are no silver bullet.
