More generally, Kubernetes is an abstraction layer between your application and hardware/cloud that allows you to declaratively define what your app is, how it runs, where it runs and what dependencies it needs. All in a standardized format that allows versioning and easy modification.
As opposed to the old-school method of having to describe all that in words to an ops team (or not and just expecting them to figure it out): "This is a Java app. It needs JDK 1.6 and at least 1GB of RAM. It expects to write logs at /var/log/foo.log. It needs a MySQL database and Redis and Elasticsearch at configured hostnames and ports. We need to run at least 6 instances horizontally scaled behind a load balancer."
As opposed to the old-school method of having to describe all that in words to an ops team (or not and just expecting them to figure it out): "This is a Java app. It needs JDK 1.6 and at least 1GB of RAM. It expects to write logs at /var/log/foo.log. It needs a MySQL database and Redis and Elasticsearch at configured hostnames and ports. We need to run at least 6 instances horizontally scaled behind a load balancer."