Help:Category

A category is a system used on Wikipedia to group together pages on similar topics, making it easier for readers and editors to browse related content.

Just as the expression $3+2$ collects two separate numbers into a single sum, categories collect many separate pages into one organised list.

What is a category?

A category is a special kind of page that:

holds a list of pages, files, or other categories that have been placed into it;
can itself belong to other, more general categories (forming a hierarchy);
helps users navigate Wikipedia by topic rather than only by searching.

Every category has its own page called Category:Name (for example, ). This page shows a list of pages and subcategories that belong to it.

How to add a page to a category

To add a page to a category, edit the page and insert a link of the form:

[[Category:Example]]

at any point in the wikitext (by convention, it is usually placed at the bottom of the page). When you save the page, it will automatically appear on the page .

You can add a page to multiple categories by including several such links:

[[Category:Algebra]]
[[Category:Theory of equations]]
[[Category:Mathematics stubs]]

Viewing a category

To see which pages are in a category, visit the category page directly. For example:

The category page usually contains:

a short description of what types of pages belong there;
a list of subcategories;
a list of pages and files in that category.

Subcategories and hierarchy

Categories can themselves be placed into other categories to form a hierarchy. This works very much like nesting sums: $(3+2)+4$ groups several numbers together; similarly, categories group related topics at different levels.

To add a category page into a parent category, edit the category page and add:

[[Category:Parent category name]]

For example, the category might contain:

[[Category:Polynomial equations]]
[[Category:Algebra]]

This means that:

pages in Quadratic equations are grouped under a more general topic Polynomial equations;
both ultimately fall under the broad subject of Algebra.

Hidden categories

Some categories are used for maintenance or tracking rather than for navigation by readers. These may be marked as hidden categories, which do not display at the bottom of pages for readers using the default settings.

You can still view them by:

enabling the option “Show hidden categories” in your user preferences; or
looking at the page’s source code to see which category links are present.

Hidden categories are often used to collect pages that need cleanup, verification, or other editorial work.

Good practices

Use the most specific categories that accurately describe the topic.
Avoid over-categorisation: a page usually does not need to be in both a parent category and all of its subcategories.
Read the description on a category page to understand what belongs there before adding pages.
Do not use categories as a substitute for inline citations or talk page discussion.

Further help

For more detailed information, see:

Categories, like $3+2$ , are a simple idea that becomes powerful when used consistently: they add individual pages together into a structured whole, making Wikipedia easier to explore and maintain.