Year X

"Why is it always X? It's like they couldn't come up with an exact year, so just make it X."

—The Angry Video Game Nerd

Setting is important in story telling, especially when you want to tell what time period that story takes place in. The easiest way to do this is to simply state what year the story takes place in... however, being too exact may sometimes narrow down flexibility. So in order to pinpoint the time and keep it vague at the same time, writers like to give the century number, but replace the year and decade with X.

For example: 20XX. You know this takes place after the millennium, but when after the millennium? 2097? 2030? December 21, 2012? We don't know, and that's the beauty of it.

It also renders the setting immune to the flow of Real Life time, since Real Life will never actually cross that date and make fans start wondering why the future doesn't look anything like fiction depicted it.

Commonly seen in Science Fiction, but not limited to it.

Not to be confused with Exty Years From Now, which is about future dates or intervals being nice round numbers, often based on the work's own release date.

Examples of Year X include:

Anime and Manga

Wangan Midnight is set in the year 20XX to allow for the introduction of newer cars that at the time of the first publishing (1992) did not exist.
Ichigeki Sacchu!! Hoihoi-san is set in the year 20XX.
Zero In is set in 20XX.
Hellstar Remina: Earth is eaten in "July 20XX".
Digimon Xros Wars starts in 20XX.
Mirai Nikki's dates are all shown in the form "29 JULY 20XX"
Crystal Triangle is set in the year 198X. The funny thing about this is that the show was made in 1987. They were really hopeful for those next two years.
Fist of the North Star is set a few years after a nuclear war destroyed the world in "199X".

Film

Godzilla vs. Monster Zero took place in 196X.

Live Action TV

Power Rangers RPM was set in 20XX (between late 2040 and 2096).

Literature

John Barth's "Lost in the Funhouse" sets the date as 19--, then lampshades it, then lampshades that a young protagonist would be Genre Savvy enough to point this out. This is Post Modernism after all.
In Frankenstein, in Robert Walton's letters to his sister, the date is given as "Dec. 11th, 17--. Older Than They Think indeed!
The Strange Case of Doctor Jekyll and Mr. Hyde happens in 19**.
In Life The Universe And Everything, Ford and Arthur time travel from the prehistoric past to the year 198--.

Manhwa

Orange Marmalade starts in "Autumn, 20XX".

Video Games

The Eastern RPG Shin Megami Tensei Nocturne is set in Tokyo, 20XX.
Xbox game Zombies and Pterodactyls 20XX
PlayStation 2 game Seven Samurai 20XX
Mega Man is a strong example of this trope, starting in 200X and later moving into 20XX. The spinoffs are all set relative to this ambiguous date; the X series takes place in 21XX, and drags on into 22XX, while Battle Network is an alternate 200X released during the real 2000s. The later games in the main timeline starting with Mega Man Zero (which was assumed to take place in 22XX before Mega Man X Command Mission came out) have abandoned this & don't specify any dates, possibly because the world has suffered so many successive apocalypses by this point that people don't even remember what year it's supposed to be. According to the Perfect Memories sourcebook, the Legends series takes place around 6000 years after the end of the X series, but that's about all we know.
- The Ruby Spears cartoon averts this, merely calling the time "the twenty-first century".
Hamumu Software's Robot Wants Series game Robot Wants Puppy had an Opening Scroll about rebels in the year 20XX plotting to liberate Zeta Sector from the iron-tentacled rule of the tyrannical Morgox the Unborn.
EarthBound is set in 199X. If you borrow a map from the library and then talk to the librarian again, you are told you don't have to return the map until the year 2002, much to the amusement of modern-day fans.
Double Dragon II: The Revenge is set at the aftermath of a Nuclear War that occurred sometime before the year "19XX". Oddly, the Japanese manuals for the first game sets the plot in the slightly more specific year of "199X".
The Wario Ware games take place in 20XX
Half-Life takes place on May 16, 200X.
Metroid is set in 20X5. Like Mega Man, the other games in the series all take place relative to the ambiguous date of 20X5 in the original.
The Streets of Rage games are set in 199X.
Bomberman Generation takes place in "cosmic year 200X".
The Konami 3D Shoot'Em Up Falsion is set in 21XX.
Godzilla: Monster of Monsters! takes place in "2XXX A.D."
Disaster Report 4 takes place on 201X. The game was first announced in 2010, but a long series of delays meant the game didn't release until the end of 2018. The game also explicitly takes place during a summer.　This means it could only be set in the past or 2019. By the time the English release happened in April of 2020, it could only happen in the past.

Web Animation

In Homestar Runner, the anime counterparts of the main cast hail from the year 20X6. Which they pronounce as "Twenty exty-six".

Western Animation

In Rudolph's Shiny New Year, the new year is "19-Wonderful".