[5112] Changes after review:

 - lines wrapped to 100 columns (according to our coding guidelines)
 - explained what @3 means in bison
 - created link to wiki page about regenerating parser code
 - added terminology page that explains what CA and D2 are
 - corrected order of the files in Makefile.am

doc/Makefile.am

 SUBDIRS = guide design
 
 EXTRA_DIST  = version.ent.in Doxyfile Doxyfile-xml
+EXTRA_DIST += devel/bison.dox
 EXTRA_DIST += devel/config-backend.dox
 EXTRA_DIST += devel/contribute.dox
 EXTRA_DIST += devel/mainpage.dox
+EXTRA_DIST += devel/terminology.dox
 EXTRA_DIST += devel/unit-tests.dox
-EXTRA_DIST += devel/bison.dox
 
 nobase_dist_doc_DATA  = examples/ddns/sample1.json
 nobase_dist_doc_DATA += examples/ddns/template.json

doc/devel/mainpage.dox

@@ -119,6 +119,7 @@
  *   - @subpage cplSignals
  *
  * @section miscellaneousTopics Miscellaneous Topics
+ * - @subpage terminology
  * - @subpage parser
  * - @subpage logKeaLogging
  *   - @subpage logBasicIdeas

doc/devel/terminology.dox

+// Copyright (C) 2017 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+/**
+@page terminology Terminology
+
+This page explains some common abbreviations and terms:
+
+- CA - Control Agent. That's a separate module that talks with Kea DHCPv4, DHCPv6 (and soon also D2)
+  over control channel and exposes their internal commands using RESTful interface.
+
+- D2 - This is a nickname of DHCP-Dynamic DNS server module. Since using the full name is awkward,
+  we often use shortened version of it: D2.
+
+- DHCP - Dynamic Host Configuration Protocol. There are two similar, but operationally different
+  protocols: DHCPv4 and DHCPv6. When v4 or v6 is not specified, the DHCP expression applies to both.
+
+- DHCPv4 - Dynamic Host Configuration Protocol for IPv4, a protocol that defines how IPv4 hosts can
+  obtain IPv4 addresses and other configuration from the servers. Defined in RFC2131.
+
+- DHCPv6 - Dynamic Host Configuration Protocol for IPv6, a protocol that defines how IPv6 hosts and
+  router can obtain IPv6 addresses, IPv6 prefixes and other configuration from the servers. Defined
+  in RFC3315.
+
+*/