A definition list can be used to format a list of terms and definitions, such as would be found in a dictionary. It is one of the few standard HTML elements that includes an information pairing; between the definition term <dt> and definition description <dd>.
Definition lists are often used when formatting search results; at a semantic level the webpage title is the ‘term’ and the page extract the ‘description’.
<dl>
<dt>Term one</dt>
<dd>Definition one</dd>
<dt>Term two</dt>
<dd>Definition two</dd>
<dt>Term three</dt>
<dd>Definition three</dd>
</dl>
A ordered list can be used to format a series of items to indicate a specific hierarchy; e.g. rank or process.
<ol>
<li>First item</li>
<li>Second item</li>
<li>Third item</li>
</ol>
An unordered list can be used to format a series of items with no specific hierarchy.
<ul>
<li>Item</li>
<li>Item</li>
<li>Item</li>
</ul>
elements/tags, semantic markup