Which of the following formats is used to describe data without formatting Web pages?

The selected answer, Extensible Markup Language (XML), is correct because XML is designed primarily for the storage and transport of data in a structured manner, without any associated formatting for display. It allows users to create custom tags and structures to represent complex data while remaining human-readable and machine-readable.

XML is fundamentally different from HTML, which is intended for displaying content in a web browser and focuses on formatting elements for rendering graphical elements. In contrast, XML serves to separate the data from the presentation, enabling data to be well-defined and easily shared across different systems regardless of how it will be formatted for end-users.

JavaScript Object Notation (JSON) is also a format used for data interchange and is lightweight, often used in APIs for web applications. While JSON and XML both focus on data representation, XML's broader capabilities for complex document structures make it the more comprehensive option for describing arbitrary data. Cascading Style Sheets (CSS) specifically deal with the presentation layer of web content and do not describe data structures at all.

By focusing on the description of data without formatting, XML stands out as the suitable choice in this context.