Why one-word tweets from brands briefly took over social media

"trains."

That's the single, lowercase word that kicked off a flurry of one-word tweets from brands and average Twitter users alike on Thursday.

The meme, labeled as "Brands Tweeting One Word" on the meme database Know Your Meme, was part of a viral marketing campaign by verified companies on Twitter.

Brands used the trend to describe themselves in a single word.

Know Your Meme credits Amtrak as the first to tweet the meme, using just the word "trains," before other verified companies jumped into the fray.

Wendy's tweeted: "burgers."

NPR tweeted: "radio."

Dr. Pepper tweeted: "soda."

FedEx tweeted: "packages."

By the end Thursday, even President Joe Biden had joined in on the meme. He tweeted: "democracy."

Some of the brand tweets racked up massive engagement for the accounts. Amtrak's initial tweet was liked more than 163,000 times.

Although the meme exploded in popularity on Thursday, Know Your Meme has documented even earlier iterations.

A tweet posted in 2020 by the official San Francisco Bay Area Rapid Transit account also read: "trains."

The bit is also reminiscent of the "Ed Balls" meme. Ed Balls was a British politician who, in 2011, accidentally tweeted his own name. Know Your Meme reports Balls was attempting to search for his name when the accidental tweet happened.

In the U.K., some British users recognize the anniversary or the tweet and Balls himself even signed a copy of the famous tweet to be auctioned for a fundraising event.

By Thursday evening, the one-word tweet had morphed to include edits of tweets, made by some users of politicians and public figures.

For example, some users edited an image to make it appear a politician they didn't like had tweeted the word "corrupt."

And while some brands embraced the trend, other Twitter users found it more annoying than amusing.

"It’s been about an hour and the one word tweet from brands trend is the most annoying thing to happen on twitter in months," one Twitter user wrote Thursday.

"what’s this one-word tweet trend. you guys are so annoying," another user wrote.

On Friday morning, Amtrak had just this to add on Twitter: "yesterday was weird. anyway it’s still trains."

This article was originally published on NBCNews.com