Tweak glossary entry for kube-apiserver (#16294)

* Retitle glossary entry for kube-apiserver

* Reword kube-apiserver glossary entry

content/en/docs/reference/glossary/kube-apiserver.md

@@ -1,19 +1,23 @@
 ---
-title: kube-apiserver
+title: API server
 id: kube-apiserver
 date: 2018-04-12
 full_link: /docs/reference/generated/kube-apiserver/
 short_description: >
-  Component on the master that exposes the Kubernetes API. It is the front-end for the Kubernetes control plane. 
+  Control plane component that serves the Kubernetes API.
 
-aka: 
+aka:
+- kube-apiserver
 tags:
 - architecture
 - fundamental
 ---
- Component on the master that exposes the Kubernetes API. It is the front-end for the Kubernetes control plane. 
+ The API server is a component of the Kubernetes
+{{< glossary_tooltip text="control plane" term_id="control-plane" >}} that exposes the Kubernetes API.
+The API server is the front end for the Kubernetes control plane.
 
-<!--more--> 
-
-It is designed to scale horizontally -- that is, it scales by deploying more instances. See [Building High-Availability Clusters](/docs/admin/high-availability/).
+<!--more-->
 
+The main implementation of a Kubernetes API server is [kube-apiserver](/docs/reference/generated/kube-apiserver/).
+kube-apiserver is designed to scale horizontally&mdash;that is, it scales by deploying more instances.
+You can run several instances of kube-apiserver and balance traffic between those instances.