Add CSI and Flexvolume to glossary (#9666)

content/en/docs/reference/glossary/csi.md

@@ -0,0 +1,21 @@
+---
+title: Container Storage Interface (CSI)
+id: csi
+date: 2018-06-25
+full_link: https://kubernetes.io/docs/concepts/storage/volumes/#csi
+short_description: >
+    The Container Storage Interface (CSI) defines a standard interface to expose storage systems to containers.
+
+
+aka: 
+tags:
+- storage 
+---
+ The Container Storage Interface (CSI) defines a standard interface to expose storage systems to containers.
+
+<!--more--> 
+
+CSI allows vendors to create custom storage plugins for Kubernetes without adding them to the Kubernetes repository (out-of-tree plugins). To use a CSI driver from a storage provider, you must first [deploy it to your cluster](https://kubernetes-csi.github.io/docs/Setup.html). You will then be able to create a {{< glossary_tooltip text="Storage Class" term_id="storage-class" >}} that uses that CSI driver.
+
+* [CSI in the Kubernetes documentation](https://kubernetes.io/docs/concepts/storage/volumes/#csi)
+* [List of available CSI drivers](https://kubernetes-csi.github.io/docs/Drivers.html)