Deployment: a grouping of functionally identical pods that can be launched and managed together. These duplicate pods allow you to achieve the resiliency and scalability that Kubernetes is designed to foster: traffic may be balanced between them as needed, and if a pod goes down, it can be immediately replaced.
The Deployment Object draws upon the Pod as well as another important abstraction: the ReplicaSet. This defines the number of duplicate Pods the system should maintain.
It is perfectly possible to write a manifest for a ReplicaSet, just as it is possible to write a manifest for a Pod—but the beauty of the Deployment is that it joins those two objects so you can create, delete, update, replicate, and otherwise manage groupings of Pods through a single interface.