Here's an example. Let's say that you don't know how open source works, and I told you the following:

Why are you in Lemmy? It's open source so any hacker can screw with it, and infect your computer with viruses. You'll never know, right?

That's FUD: fear, uncertainty, and doubt. It's a disingenuous tactic to convince you to not do something, based on the following:

• You fear a certain outcome. In this case, a computer virus.
• That fear is vaguely associated with something that is uncertain for you. In this case, how a hacker could use Lemmy to inject viruses into your computer.
• The odds of that outcome happening are doubtful; it may happen, it may not, otherwise you could call me out for not happening. In this case, even if you don't get a virus from using Lemmy, I can still say "well, some people get it, some don't, but let's play it safe and avoid Lemmy."

This shitty strategy is fairly used in the tech industry because most people are clueless about tech, but they know that it has a big impact on their lives. However you'll also see this in politics, religious debate (Pascal's Wager is FUD), and others.

Fear. Uncertainty. Doubt.

It’s sometimes used as a noun for things that cause FUD, too.

As others have said Fear, Uncertainty, Doubt.

It entered tech lingo way back in the 90s when Microsoft was fighting an early wave of Linux on desktop. They would troll and present themselves as a reliable alternative.

They weren't the first to do it. IBM's unofficial motto in the 70s was "nobody gets fired for going with IBM".

Guess you’re one of today’s lucky 10000

Fear, uncertainty, and doubt

In a modern internet context:

Fear. Uncertainty. Doubt.

Often used in crypto circles when a shitty project is being accused of being a rug pull. The scammer may say "it's just FUD, ignore it".

On 'the street', if I called someone a fud, it is calling them an idiot.

Others have answered it pretty well, but here's a more specific example:

In the long, long ago, IBM was the biggest seller of computer equipment, and by a wide margin. They alone decided the majority of standards in use, as well as what was coming soon. Anticompetitive monopoly tactics were standard there. For the vast majority of customers, you absolutely HAD to be compatible with whatever IBM was selling.

When one of IBM's competitors would introduce a new and desirable product, IBM would often issue a press release. They would say that they have something similar in the works, and it won't be compatible with the other brand. The safe option would be to wait for IBM to release theirs rather than take a risk on a whole new ecosystem. This was all despite the fact that IBM never actually had said product in development.

As a result, the customers would be afraid of being stuck on something incompatible, with an uncertain future. They wouldn't buy it, but they would continue to buy their existing IBM options. Eventually the other product would fold (proving their fears correct), and they'd forget what IBM promised.

It means "Fear, Uncertainty, Doubt".

It's a modern kind of shit talking employed by large corporations in conjunction with astro turfing (pretending to be an unbiased commentator, when you're really as biased as can be) to dissuade people from going to a competitor.

Because saying stuff like "I dunno dude, there's been reports of a lot of problems with Product X" is a lot more persuasive than "Product X sux!!!", especially when you don't know the poster was paid by Company Y, a competitor, to say it.

Or in Glasgow...

I had to look this up the other day and found it annoying. Absolutely feels like something not common enough to abbreviate to me

In what context is this? I have never heard of FUD before in my life. Why the heck does Fear, Uncertainty, Doubt need to be arranged into an acronym?

We don't sell Duff here, we sell Fudd!

Bullshit people push to agree with their viewpoints that make other things look bad/scary/insecure/etc

I keep thinking it’s FOD (foreign object damage) which is why you don’t want small, hard objects on a runway or something. Stuff like bullet casings can get sucked into a jet engine, and cause FOD that takes a plane out of service.

Then I notice that FOD doesn’t make any sense in context, reread the sentence, and realize it’s FUD. Whoops.

Flowers Ultimately Die.

The best thing about abbreviations is that they are entirely contextual, which means that if it isn't obvious what's meant, you can make up your own meaning and wonder/ask why the other person is using it so very wrong.

There's even an abbreviation for it: TLB, which in this context means Three Letter Bullshit.

Was it quicker to make a post asking random people on the internet, and waiting for a factual response, than to type the same question into a search engine?

Elmer Fud ?

oh we fucking
we fucking alright