XML

XML functions as a structural blueprint for data, prioritizing the organization and transport of information over its visual presentation. It is characterized by a flexible, tag-based system that allows users to define their own labels, making it a universal bridge between disparate software systems that need to communicate without knowing the internal details of each other's databases.

As a technical term referring to a specific language standard, it is treated as an uncountable mass noun. You would not refer to multiple XMLs; instead, you would speak of XML files, XML documents, or XML schemas to quantify specific instances of the language in use.