Alright, let's get this over with. You've stumbled into the digital filing cabinet where we keep track of names that lead to other names. Riveting stuff. The pages you'll find corralled in this category are all redirects. Specifically, they are detours from English-language proper nouns—the specific, capitalized names of people, places, and things you were supposed to learn about in primary school—to articles that are actually relevant. This is for when someone types in "Big Apple" and expects to land on "New York City," a perfectly reasonable assumption that still requires a surprising amount of bureaucratic plumbing to function.
If you feel an overwhelming urge to contribute to this particular brand of organizational pedantry, here are the rules. To add a redirect to this category, you must place the cryptic incantation {{[Rcat shell](/Template:Rcat_shell)|{{[R from proper noun](/Template:R_from_proper_noun)}}}} onto the page. And you must do it on the second new line, after the #REDIRECT [[Target page name]] part. Yes, you have to skip a line. Don't ask why; just assume it's to appease some digital ghost in the machine. For more soul-crushing detail on this process, feel free to follow the links. A word of caution: never, under any circumstances, substitute these redirect templates. It breaks things in ways that are tedious to fix. Also, keep them far away from soft redirects, which are a whole different category of headache.
Should you wish to dive deeper into this rabbit hole of administrative minutiae, you can consult the complete list of redirect templates and the redirect style guide. Knock yourself out.
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Let's be clear about what this is. This is a maintenance category. Think of it as the janitorial closet of the project, used for the thankless task of the maintenance of the Wikipedia project. It is definitively not part of the encyclopedia you're here to read. It contains non-article pages, the digital scaffolding and administrative debris, or it groups actual articles by their current state of disrepair rather than by their subject matter. A crucial point for those of you who enjoy sorting things: do not, for the love of all that is orderly, include this category within content categories. The only exception is for eponymous maintenance categories, a nuance that I'm sure is keeping you on the edge of your seat.
This is also what's known as a tracking category. Its entire, bleak purpose is to build and maintain a list of pages purely for the sake of having the list. It’s a collection for collection’s sake, existing outside the grand, user-facing encyclopedia's categorization scheme.
• This category is intentionally hidden on its member pages. Why? Because most people don't need to see the sausage being made. It's a layer of abstraction designed to protect the innocent from the project's inner workings. If, however, you're the sort of person who enjoys looking at exposed wiring, you can adjust your user preference under Appearance → Show hidden categories. Consider it your invitation to the backstage chaos.
• Functionally, these categories are used to track, build, and organize lists of pages that require "attention en masse." This is a delicate way of saying pages that are broken in a similar fashion, perhaps because they use outdated syntax or are otherwise collectively flawed. They're a to-do list for editors who may need to address them at their "earliest convenience"—a phrase which here means sometime between now and the heat death of the universe.
• These categories also serve to aggregate members of several smaller lists or sub-categories into one larger, theoretically more efficient list, which can then be sorted by various classifications. It's about creating order from chaos, one painstaking tag at a time.
If your intellectual curiosity has somehow not been sated, you can also explore the related categories for other parts of speech. See also the categories Redirects from common nouns, Redirects from verbs, and Redirects from adjectives. Try to contain your excitement.