diff --git a/dump/kubernetes/README.md b/dump/kubernetes/README.md
index f37ef04..598f673 100644
--- a/dump/kubernetes/README.md
+++ b/dump/kubernetes/README.md
@@ -3,5 +3,5 @@ Some notes on Kubernetes.
 - [Some stupid basics](./stupid-basics.md)
 - [Deployment strategies](./deployment-types.md)
 - [Volumes](./volumes.md)
-- [CSI](./csi.md)
-- [CRD](./crd.md)
+- [Container Storage Interface (CSI)](./csi.md)
+- [Custom Resource Definition (CRD)](./crd.md)
diff --git a/dump/kubernetes/crd.md b/dump/kubernetes/crd.md
index f37254e..08b8a33 100644
--- a/dump/kubernetes/crd.md
+++ b/dump/kubernetes/crd.md
@@ -1,2 +1,28 @@
+## Custom Resource
+
+Custom resources are extensions of the Kubernetes API.
+
+They are not available in a default Kubernetes installation
+and have to be installed/created separately.
+
+All requests are coming to the API server as usual.
+
+### Custom Resource Definition (CRD)
+
+CRD is a way to define a custom resource.
+
+To work with CRD, you need to create a Custom Controller to handle
+CRD requests, because the API server doesn't know how your CRD
+should behave in different situations.
+
+### Controller vs Operator
+
+Controller works on vanilla Kubernetes objects.
+
+Operator is a controller that works with custom resources.
+
+### Resources
+
+- https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/
+- https://kubernetes.io/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/
 
-todo: add more info
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