A termdef is an inline term definition. Some styles of documentation collect all terms together in a glossary of some sort, but another style is to place the definitions inline.

The glossary and glosslist elements support the former style, termdef the latter.

Every term should have an xml:id attribute to uniquely identify it. The content of the termdef is the definition of the term. Often it is valuable to word the definition so that it will stand alone, in case it becomes useful to extract all the terms into a separate glossary in addition to having them defined inline.

Every termdef must contain exactly one firstterm. The firstterm identifies the actual term defined by the termdef.

<article xmlns="http://docbook.org/ns/docbook"
	 xmlns:xlink='http://www.w3.org/1999/xlink'>
<title>termdef</title>

<para>
  This paragraph contains an inline term definition.
  <termdef xml:id="dt-xml-processor">A software module
  called an <firstterm>XML processor</firstterm> is used
  to read XML documents and provide access to their
  content and structure.</termdef> The definition comes
  from <link xlink:href="http://www.w3.org/TR/REC-xml">the
  XML Recommendation</link>.
</para>

</article>

This paragraph contains an inline term definition. [Definition: A software module called an XML processor is used to read XML documents and provide access to their content and structure.] The definition comes from the XML Recommendation.