<dl>

dl represents a defined formatted list which consists of two parts: a term (or, title) and a description. The term is given by the dt element and is restricted to inline/phrasing content; the description is given with a dd element that may contain block-level content and/or inline/phrasing.

HTML 5 refers to the dt element as name and dd element as a value.

A definition list which—Essentially—is a container must have at least one dt element and it must have at least one dd element. However, any combination may be used. Though, semantic arguments require that the dt element precede the dd value.

Lastly, HTML 4.01 has as a suggestion that the dl element may be used for dialogues.

Start tag:
<dl>
End tag:
</dl>
Example [Basic]:
Pandora’s Paintbox
That which she did not open to find her watercolors.
Code [HTML]:

<dl>
<dt>Pandora’s Paintbox</dt>
<dd>That which she did not open to find her watercolors.</dd>
</dl>
Example [Basic (FAQ Format)]:
Where is Borneo located?
Borneo is an island which may be found surrounded by water: the South China Sea, the Sulu Sea, the Celebes Sea, the Makassar Strait, the Java Sea and the Karimata Strait.
The Malay Peninsula, Sumatra, Java, Sulawesi and the Philippines are the closest landmasses.
What language do Flying Monkeys speak?
Malayo-Polynesian variants.
Code [HTML]:

<dl>
<dt>Where is Borneo located?</dt>
<dd>Borneo is an island which may be found surrounded by water: the South China
Sea, the Sulu Sea, the Celebes Sea, the Makassar Strait, the Java Sea and the
Karimata Strait.</dd>
<dd>The Malay Peninsula, Sumatra, Java, Sulawesi and the Philippines are the closest
landmasses.</dd>
<dt>What language do Flying Monkeys speak?</dt>
<dd>Malayo-Polynesian variants.</dd>
</dl>
Example [Basic (Dialogue)]:

Scene—Morning-room in Algernon’s flat in Half Moon Street. The room is luxuriously and artistically furnished. The sound of a piano is heard in the adjoining room.

[Lane is arranging afternoon tea on the table, and after the music has ceased, Algernon enters.]

Algernon.
Did you hear what I was playing, Lane?
Lane.
I didn’t think it polite to listen, sir.
Algernon.
I’m sorry for that, for your sake. I don't play accurately—anyone can play accurately—but I play with wonderful expression. As far as the piano is concerned, sentiment is my forte. I keep science for Life.
Lane.
Yes, sir.
Algernon.
And, speaking of the science of Life, have you got the cucumber sandwiches for Lady Bracknell?
Lane.
Yes, sir. [Hands them on a salver.]
Algernon [Inspects them, takes two, and sits down on the sofa].
Oh!...by the way, Lane, I see from your book that on Thursday night, when Lord Shoreman and Mr. Worthington were dining with me, eight bottles of champagne are entered as having been consumed.
Lane.
Yes, sir; eight bottles and a pint.
Code [HTML]:

<dl>
<dt class="declaratoryTitle">Algernon.</dt>
<dd>Did you hear what I was playing, Lane?</dd>
<dt class="declaratoryTitle">Lane.</dt>
<dd>I didn’t think it polite to listen, sir.</dd>
<dt class="declaratoryTitle">Algernon.</dt>
<dd>I’m sorry for that, for your sake. I don't play accurately—anyone can »
play accurately—but I play with wonderful expression. As far as the piano »
is concerned, sentiment is my forte. I keep science for Life.</dd>
<dt class="declaratoryTitle">Lane.</dt>
<dd>Yes, sir.</dd>
<dt class="declaratoryTitle">Algernon.</dt>
<dd>And, speaking of the science of Life, have you got the cucumber sandwiches »
for Lady Bracknell?</dd>
<dt class="declaratoryTitle">Lane.</dt>
<dd>Yes, sir. [<span class="oblique">Hands them on a salver.</span>]</dd>
<dt class="declaratoryTitle">Algernon [<span class="oblique textTransformNone">Inspects »
them, takes two, and sits down on the sofa</span>].</dt>
<dd>Oh!...by the way, Lane, I see from your book that on Thursday night, »
when Lord Shoreman and Mr. Worthington were dining with me, eight »
bottles of champagne are entered as having been consumed.</dd>
<dt class="declaratoryTitle">Lane.</dt>
<dd>Yes, sir; eight bottles and a pint.</dd>
</dl>
Example [Complex]:
Element-Type:
List
Attributes:
Code [HTML]:

<dl id="elementType">
<dt>Element-Type:</dt> 
<dd>List</dd>
<dt>Attributes:</dt>
<dd>
<ul id="elementAttributes">
<li><a href="/html-identifiers/html-identifier-id-attribute">id</a>;</li>
<li><a href="/html-identifiers/html-identifier-class-attribute">class</a></li>
<li><a href="/html-element-attributes/html-language-code-attribute">lang</a></li>
<li><a href="/html-element-attributes/text-direction-attribute">dir</a></li>
<li><a href="/html-element-attributes/title-attribute">title</a></li>
<li><a href="/html-element-attributes/html-style-attribute">style</a></li>
</ul>
</dd>
</dl>
Notes:

HTML 4.01 (and, by extension, XHTML 1.0) states that a definition list is comprised with at least one dt element and at least one dd element. However, definition lists which do not include either one dt or one dd will pass HTML Validation. Whereas, HTML 5 Validation fails when either element is missing.

  1. HTML 4.01/Strict passes HTML Validation. See Definition List DD Missing [HTML 4.01/Strict].
  2. XHTML 1.0/Transitional passes HTML Validation. See Definition List DD Missing [XHTML 1.0/Transitional].
  3. XHTML 1.0/Strict passes HTML Validation. See Definition List DD Missing [XHTML 1.0/Strict].
  4. HTML 5 fails HTML Validation. See Definition List DD Missing [HTML 5].
Element-Type:
List
Attributes:

</dl>