Acronym. eXtensible Markup Language. XML is a file format which is commonly used for:
XML and HTML are related, as they use a similar syntax, however, XML uses a much stricter syntax.
XML looks like HTML:
<products> <product name="dog food" upc="541231212567"> <prices> <price currency="USD">53.33</price> <price currency="EUR">21.99</price> </prices> <name>Zug Zug Dog Food</name> <description> <![CDATA[ This is the only kind of food that won't eat. ]]> </description> </product> </products>
But it can be associated with a DTD (Data Type Definition) which then defines what tags and attributes are permitted.