Add "workload" to glossary (kubernetes#12622)

* Add "workload" to glossary

* Use en_US spelling of "fulfill"

* Revise short description

Co-Authored-By: Tim Bannister <tim@scalefactory.com>

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

@@ -0,0 +1,28 @@
+---
+title: Workload
+id: workload
+date: 2019-02-12
+full_link: /docs/concepts/workloads/
+short_description: >
+  A set of applications for processing information to serve a purpose that is valuable to a single user or group of users.
+
+aka:
+tags:
+- workload
+---
+A workload consists of a system of services or applications that can run to fulfill a
+task or carry out a business process.
+
+<!--more-->
+
+Alongside the computer code that runs to carry out the task, a workload also entails
+the infrastructure resources that actually run that code.
+
+For example, a workload that has a web element and a database element might run the
+database in one {{< glossary_tooltip term_id="StatefulSet" >}} of
+{{< glossary_tooltip text="pods" term_id="pod" >}} and the webserver via
+a {{< glossary_tooltip term_id="Deployment" >}} that consists of many web app
+{{< glossary_tooltip text="pods" term_id="pod" >}}, all alike.
+
+The organisation running this workload may well have other workloads that together
+provide a valuable outcome to its users.