"The ability to move applications and data from one cloud provider to another. Each cloud provider has a certain level of integration and lock-in that may not be available in another provider. Take for example AWS Lambda functions. These are serverless applications that run exclusively in AWS, and if moving to Google Cloud Functions, may need to be re-written slightly to work in the Google Cloud Platform. To ensure cloud portability, the cloud community are designing architectural patterns that give developers guidelines for how to design their applications, such that it can be run in any cloud, without having to rebuild their systems. A good example of a popular architecture and technology is Kubernetes. Kubernetes allows applications to be portable between clouds."
in other words
Being able to change where you live online.