WBW
Wayback Wednesday
Example

A WBW post from Twitter
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Usage
Last Updated: January 6, 2022
With best wishes
Friends, parents, and other loved ones may use WBW (with best wishes) to wish you well at the end of an email. This acronym is used in place of other letter closings like "Regards," "Cheers," and "Yours truly."
While you may also see WBW used to mean "with best wishes" in social media messages, that usage is less common. If you see WBW in a social media post, it is more likely to mean Wayback Wednesday, which is similar to TBT.
Example
Jenny"
A girl who ends all her emails with WBW
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Usage
Last Updated: January 5, 2022
World Between Worlds
Star Wars fans use WBW as shorthand for World Between Worlds. The World Between Worlds is a mystical plane first shown in the TV show Star Wars Rebels. It connects every moment in time and space together, allowing Jedi who access it to travel in time and space.
When am I likely to see WBW used?
You're most likely to see WBW used in discussions of how (and big spoiler alert here) the character Ben Solo (aka Kylo Ren) can return from his death in Star Wars: The Rise of Skywalker. Many fans believe Ben and Rey's connection is facilitated by the WBW, and that Rey could use the WBW to somehow resurrect or retrieve Ben from a point in the past.
Example

Some SW fans' WBW theories are ... less likely than others
Related Slang
Usage
Last Updated: January 6, 2022
On Twitter, Instagram, and other social media sites, WBW stands for Wayback Wednesday. In WBW posts, users share interesting pictures and anecdotes from way back in the past.
How is WBW different than TBT?
As you may already know, social media users also post pictures and anecdotes from the past on Throwback Thursday (TBT). There's not much difference between TBT and WBW, other than that one is used on Thursday and the other on Wednesday. However, WBW posts tend to focus on items from further back in the past than TBT posts.