Final answer:
XML stands for eXtensible Markup Language, which is used to store and transport data and allows users to define custom tags.
Step-by-step explanation:
XML stands for eXtensible Markup Language. It is a markup language much like HTML, but designed to store and transport data. XML provides a format for documents containing structured information.
Structured information contains both content (words, pictures, etc.) and some indication of what role that content plays. Unlike HTML, which defines how to display data, XML defines the structure of the data. Since XML is extensible, it allows users to define their own custom tags to better suit their needs.