In Kubernetes and OpenShift, the API server provides a set of built-in objects, such as Pods, Services, and Deployments. However, every application has unique requirements, and built-in resources may not always be enough. This is where Custom Resource Definitions (CRDs) come in. A CRD allows you to define your own custom resources, just like native Kubernetes objects, and manage them using standard Kubernetes tools (kubectl or oc).