Any typical enterprise-grade application deployed on Kubernetes comprises several API resources that need to be deployed together. For example, the WordPress application, which is one of the example applications available on the Kubernetes GitHub repository, includes:

a wordpress frontend pod,
a wp-pv-claim persistent volume claim mounted to the frontend pod,
a wordpress-mysql MySQL database pod,
a mysql-pv-claim persistent volume claim mounted to the MySQL database pod,
two persistent volumes: wordpress-pv-1 and wordpress-pv-2 to serve the persistent volume claims,
services for the database and frontend pods.

Application (or app) is not a native construct in Kubernetes. However, managing applications is the primary concern of the developers and operations. Application delivery on Kubernetes involves upgrading, downgrading, and customizing the individual API resources. Kubernetes allows you to restrict the spread of your application resources through namespaces such that you can deploy an entire app in a namespace that can be deleted or created. However, a complex application might consist of resources spread across namespaces, and in such cases answering the following questions might be a challenge: