XHTML puts no constraints on where dt and dd elements appear within the dl element:

<dl>
<dt>Client</dt>

<dt>Server</dt>
<dd>A program which runs on some computer in a network</dd>
<dd>A program or computer providing some kind of service to its clients</dd>
<dd>To spend time browsing around the  Web or the Internet</dd>

<dt>Surfing</dt>
</dl>

But it can produce strange results:

Client

Server

A program which runs on some computer in a network

A program or computer providing some kind of service to its clients

To spend time browsing around the Web or the Internet

Surfing

It caters for multiple definitions of a term and terms with, currently, no definition