Add glossary entry for proxy (#16293)

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

@@ -0,0 +1,27 @@
+---
+title: Proxy
+id: proxy
+date: 2019-09-10
+short_description: >
+  An application acting as an intermediary beween clients and servers
+
+aka:
+tags:
+- networking
+---
+ In computing, a proxy is a server that acts as an intermediary for a remote
+service.
+
+<!--more-->
+
+A client interacts with the proxy; the proxy copies the client's data to the
+actual server; the actual server replies to the proxy; the proxy sends the
+actual server's reply to the client.
+
+[kube-proxy](/docs/reference/command-line-tools-reference/kube-proxy/) is a
+network proxy that runs on each node in your cluster, implementing part of
+the Kubernetes {{< glossary_tooltip term_id="service">}} concept.
+
+You can run kube-proxy as a plain userland proxy service. If your operating
+system supports it, you can instead run kube-proxy in a hybrid mode that
+achieves the same overall effect using less system resources.