What is a 'namespace' in XML?

Used to avoid name collisions of elements and attributes when merging XML documents from different sources. Declared using the xmlns attribute.

Example:

<root xmlns:m="http://example.com/markup"
      xmlns:s="http://example.com/styling">

    <m:element1>Content</m:element1>
    <s:element2 color="red">Styled content</s:element2>

</root>