Namespaces are another advanced feature of XML, outlined in a W3C note as part of the XML 1.0 specification.
They allow developers to qualify uniquely the element names and relationships and make these names recognizable, to avoid name collisions on elements that have the same name but are defined in different vocabularies.
They allow tags from multiple namespaces to be mixed, which is essential if data is coming from multiple sources. For example, a bookstore may define the <TITLE> tag to mean the title of a book, contained only within the <BOOK> element. A directory of people, however, might define <TITLE> to indicate a person's position, for instance: <TITLE>President</TITLE>.
Namespaces help define this distinction clearly.