Update glossary

docs/glossary.rst

@@ -18,3 +18,16 @@ A port is an opening on network adapter that cable plug into.
 
 For example a VM can have a serial and an ethernet adapter plugged in.
 The ethernet adapter can have 4 ports.
+
+Controller
+----------
+
+The central server managing everything in GNS3. A GNS3 controller
+will manage multiple GNS3 hypervisor.
+
+Hypervisor
+----------
+
+The process running on each server with GNS3. The GNS3 hypervisor 
+is controlled by the GNS3 controller.
+