CSS
CSS: CSS, or Cascading Style Sheets, is the stylesheet language used to control the presentation of HTML and other markup documents.
What CSS means
CSS, or Cascading Style Sheets, is the stylesheet language used to control the presentation of HTML and other markup documents. CSS rules connect selectors with declarations. It is used for typography, color, spacing, layout, responsive behavior, animation and many other aspects of visual presentation.
On production websites, the term is usually encountered as part of the browser–server model: documents and assets are requested, interpreted and presented through standardized web technologies. Correct use depends on the surrounding technology rather than on the term in isolation.
How it is used in web and design work
For designers and developers, understanding this concept helps clarify what belongs in content structure, presentation, behavior, networking or browser behavior. That separation makes interfaces easier to debug, optimize and maintain.
In practical work, CSS should be interpreted according to its technical or design context. The surrounding document structure, software, output medium, browser behavior or publishing workflow determines how the concept is applied. The purpose of the term is to describe a specific part of that process, not to replace the other concepts around it.
Where the term fits
Web terminology often describes one layer of a larger system. Markup defines document structure, CSS defines presentation, JavaScript supplies programmable behavior, networking protocols move resources, and the browser combines those inputs into an interactive page. Keeping those responsibilities separate is useful when tracing where a problem originates and which technology is responsible for correcting it.
When checking a web term in practice, use browser developer tools and standards-oriented documentation to identify the actual resource, request, DOM node, computed style or runtime behavior involved. A visual symptom does not necessarily identify its technical cause: an apparent layout problem can originate in markup, a network failure can prevent styling or scripts from loading, and script behavior can alter the document after the initial HTML has been parsed.
Why the distinction matters
A common source of confusion is treating related web terms as interchangeable. Web documents, browsers, servers, protocols and programming interfaces each describe different layers of the system.
Using precise terminology helps designers, developers, editors and clients describe the same problem without mixing separate layers of a project. That is especially useful when a visual issue may actually come from document structure, when a WordPress issue belongs to a theme or plugin, or when an image problem depends on resolution, color or file type rather than styling.
Related glossary terms
The following entries sit close to CSS in the same workflow or terminology set. The distinction is useful because each term names a separate concept:
Selector: A CSS selector is the part of a CSS rule that identifies which elements a set of declarations should apply to.
Cascade: The CSS cascade is the set of rules used to resolve which declarations apply when multiple declarations target the same property on the same element.
Specificity: Specificity is the weighting system CSS uses when competing selectors from the same cascade origin and layer match the same element.
CSS Grid: CSS Grid is a two-dimensional layout system for arranging content in rows and columns.
Sources and further reading
This entry is a concise, independently written definition based on established documentation. The linked references provide standards, product documentation or broader technical context.