Adding SNO term to glossary

Author: aireilly

contributing_to_docs/term_glossary.adoc

@@ -635,6 +635,24 @@ A service account binds together:
 * a principal that can be authenticated and authorized
 * a set of secrets
 
+''''
+=== single-node OpenShift
+
+Usage: single-node OpenShift
+
+Single-node OpenShift (or {product-title} on a single-node cluster) is a deployment footprint that provides control plane and worker node capabilities in a single server for deployments in constrained environments.
+
+Do not use: Single Node Openshift (SNO).
+
+''''
+=== three-node OpenShift
+
+Usage: three-node OpenShift
+
+Three-node OpenShift is a compact cluster deployment footprint on three nodes for deployments in constrained environments. It provides three control plane nodes that you configure as schedulable for workloads.
+
+Do not use: Three Node Openshift.
+
 ''''
 === SkyDNS